errorprone.xml

<?xml version="1.0"?>

<ruleset name="Error Prone"
    xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">

    <description>
Rules to detect constructs that are either broken, extremely confusing or prone to runtime errors.
    </description>

    <rule name="AssignmentInOperand"
          language="java"
          since="1.03"
          message="Avoid assignments in operands"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AssignmentInOperandRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#assignmentinoperand">
        <description>
Avoid assignments in operands; this can make code more complicated and harder to read.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public void bar() {
    int x = 2;
    if ((x = getX()) == 3) {
      System.out.println("3!");
    }
}
]]>
        </example>
    </rule>

    <rule name="AssignmentToNonFinalStatic"
          language="java"
          since="2.2"
          message="Possible unsafe assignment to non-final static field ''{0}'' in a constructor."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AssignmentToNonFinalStaticRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#assignmenttononfinalstatic">
        <description>
Identifies a possible unsafe usage of a static field.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class StaticField {
   static int x;
   public FinalFields(int y) {
    x = y; // unsafe
   }
}
]]>
        </example>
    </rule>

    <rule name="AvoidAccessibilityAlteration"
          language="java"
          since="4.1"
          message="You should not modify visibility of constructors, methods or fields using setAccessible()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidaccessibilityalteration">
        <description>
Methods such as `getDeclaredConstructors()`, `getDeclaredMethods()`, and `getDeclaredFields()` also
return private constructors, methods and fields. These can be made accessible by calling `setAccessible(true)`.
This gives access to normally protected data which violates the principle of encapsulation.

This rule detects calls to `setAccessible` and finds possible accessibility alterations.
If the call to `setAccessible` is wrapped within a `PrivilegedAction`, then the access alteration
is assumed to be deliberate and is not reported.

Note that with Java 17 the Security Manager, which is used for `PrivilegedAction` execution,
is deprecated: [JEP 411: Deprecate the Security Manager for Removal](https://openjdk.java.net/jeps/411).
For future-proof code, deliberate access alteration should be suppressed using the usual
suppression methods (e.g. by using `@SuppressWarnings` annotation).
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall[
          pmd-java:matchesSig("java.lang.reflect.AccessibleObject#setAccessible(boolean)")
       or pmd-java:matchesSig("_#setAccessible(java.lang.reflect.AccessibleObject[],boolean)")
    ]
    [not(ArgumentList/BooleanLiteral[@True = false()])]
    (: exclude anonymous privileged action classes :)
    [not(ancestor::ConstructorCall[1][pmd-java:typeIs('java.security.PrivilegedAction')]/AnonymousClassDeclaration)]
    (: exclude inner privileged action classes :)
    [not(ancestor::ClassOrInterfaceDeclaration[1][pmd-java:typeIs('java.security.PrivilegedAction')])]
    (: exclude privileged action lambdas :)
    [not(ancestor::LambdaExpression[pmd-java:typeIs('java.security.PrivilegedAction')])]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;

public class Violation {
    private void invalidSetAccessCalls() throws NoSuchMethodException, SecurityException {
        Constructor<?> constructor = this.getClass().getDeclaredConstructor(String.class);
        // call to forbidden setAccessible
        constructor.setAccessible(true);

        Method privateMethod = this.getClass().getDeclaredMethod("aPrivateMethod");
        // call to forbidden setAccessible
        privateMethod.setAccessible(true);

        // deliberate accessibility alteration
        String privateField = AccessController.doPrivileged(new PrivilegedAction<String>() {
            @Override
            public String run() {
                try {
                    Field field = Violation.class.getDeclaredField("aPrivateField");
                    field.setAccessible(true);
                    return (String) field.get(null);
                } catch (ReflectiveOperationException | SecurityException e) {
                    throw new RuntimeException(e);
                }
            }
        });
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidAssertAsIdentifier"
          language="java"
          maximumLanguageVersion="1.3"
          since="3.4"
          message="Avoid using assert as an identifier; it became a reserved word in JDK 1.4"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidassertasidentifier">
        <description>
Use of the term `assert` will conflict with newer versions of Java since it is a reserved word.

Since Java 1.4, the token `assert` became a reserved word and using it as an identifier will
result in a compilation failure for Java 1.4 and later. This rule is therefore only useful
for old Java code before Java 1.4. It can be used to identify problematic code prior to a Java update.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>//VariableDeclaratorId[@Name='assert']</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class A {
    public class Foo {
        String assert = "foo";
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidBranchingStatementAsLastInLoop"
          language="java"
          since="5.0"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidBranchingStatementAsLastInLoopRule"
          message="Avoid using a branching statement as the last in a loop."
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidbranchingstatementaslastinloop">
        <description>
Using a branching statement as the last part of a loop may be a bug, and/or is confusing.
Ensure that the usage is not a bug, or consider using another approach.
        </description>
        <priority>2</priority>
        <example>
<![CDATA[
// unusual use of branching statement in a loop
for (int i = 0; i < 10; i++) {
    if (i*i <= 25) {
        continue;
    }
    break;
}

// this makes more sense...
for (int i = 0; i < 10; i++) {
    if (i*i > 25) {
        break;
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidCallingFinalize"
          language="java"
          since="3.0"
          message="Avoid calling finalize() explicitly"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidcallingfinalize">
        <description>
The method Object.finalize() is called by the garbage collector on an object when garbage collection determines
that there are no more references to the object. It should not be invoked by application logic.

Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall[pmd-java:matchesSig("java.lang.Object#finalize()")]
    (: it's ok inside finalize :)
    [not(SuperExpression and ancestor::*[self::MethodDeclaration or self::Initializer][1][@Name = 'finalize'][@Arity = 0][VoidType])]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
void foo() {
    Bar b = new Bar();
    b.finalize();
}
]]>
        </example>
    </rule>

    <rule name="AvoidCatchingNPE"
          language="java"
          since="1.8"
          message="Avoid catching NullPointerException; consider removing the cause of the NPE."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidcatchingnpe">
        <description>
Code should never throw NullPointerExceptions under normal circumstances.  A catch block may hide the
original error, causing other, more subtle problems later on.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//CatchClause/CatchParameter/ClassOrInterfaceType[pmd-java:typeIsExactly('java.lang.NullPointerException')]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    void bar() {
        try {
            // do something
        } catch (NullPointerException npe) {
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidCatchingThrowable"
          language="java"
          since="1.2"
          message="A catch statement should never catch throwable since it includes errors."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidcatchingthrowable">
        <description>
Catching Throwable errors is not recommended since its scope is very broad. It includes runtime issues such as
OutOfMemoryError that should be exposed and managed separately.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value><![CDATA[
                //CatchParameter[ClassOrInterfaceType[pmd-java:typeIsExactly('java.lang.Throwable')]]/VariableDeclaratorId
                ]]></value>
            </property>
        </properties>
        <example>
<![CDATA[
public void bar() {
    try {
        // do something
    } catch (Throwable th) {  // should not catch Throwable
        th.printStackTrace();
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidDecimalLiteralsInBigDecimalConstructor"
          language="java"
          since="3.4"
          message="Avoid creating BigDecimal with a decimal (float/double) literal. Use a String literal"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoiddecimalliteralsinbigdecimalconstructor">
        <description>
One might assume that the result of "new BigDecimal(0.1)" is exactly equal to 0.1, but it is actually
equal to .1000000000000000055511151231257827021181583404541015625.
This is because 0.1 cannot be represented exactly as a double (or as a binary fraction of any finite
length). Thus, the long value that is being passed in to the constructor is not exactly equal to 0.1,
appearances notwithstanding.

The (String) constructor, on the other hand, is perfectly predictable: 'new BigDecimal("0.1")' is
exactly equal to 0.1, as one would expect.  Therefore, it is generally recommended that the
(String) constructor be used in preference to this one.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ConstructorCall[pmd-java:matchesSig('java.math.BigDecimal#new(double)')]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
BigDecimal bd = new BigDecimal(1.123);       // loss of precision, this would trigger the rule

BigDecimal bd = new BigDecimal("1.123");     // preferred approach

BigDecimal bd = new BigDecimal(12);          // preferred approach, ok for integer values
]]>
        </example>
    </rule>

    <rule name="AvoidDuplicateLiterals"
          language="java"
          since="1.0"
          message="The String literal {0} appears {1} times in this file; the first occurrence is on line {2}"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidDuplicateLiteralsRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidduplicateliterals">
        <description>
Code containing duplicate String literals can usually be improved by declaring the String as a constant field.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
private void bar() {
     buz("Howdy");
     buz("Howdy");
     buz("Howdy");
     buz("Howdy");
}
private void buz(String x) {}
]]>
        </example>
    </rule>

    <rule name="AvoidEnumAsIdentifier"
          language="java"
          maximumLanguageVersion="1.4"
          since="3.4"
          message="Avoid using enum as an identifier; it's a reserved word in JDK 1.5"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidenumasidentifier">
        <description>
Use of the term `enum` will conflict with newer versions of Java since it is a reserved word.

Since Java 1.5, the token `enum` became a reserved word and using it as an identifier will
result in a compilation failure for Java 1.5 and later. This rule is therefore only useful
for old Java code before Java 1.5. It can be used to identify problematic code prior to a Java update.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>//VariableDeclaratorId[@Name='enum']</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class A {
    public class Foo {
        String enum = "foo";
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidFieldNameMatchingMethodName"
          language="java"
          since="3.0"
          message="Field {0} has the same name as a method"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidfieldnamematchingmethodname">
        <description>
It can be confusing to have a field name with the same name as a method. While this is permitted,
having information (field) and actions (method) is not clear naming. Developers versed in
Smalltalk often prefer this approach as the methods denote accessor methods.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//FieldDeclaration/VariableDeclarator/VariableDeclaratorId
    [some $method in ../../..[self::ClassOrInterfaceBody or self::EnumBody]/MethodDeclaration
     satisfies lower-case(@Name) = lower-case($method/@Name)]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    Object bar;
    // bar is data or an action or both?
    void bar() {
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidFieldNameMatchingTypeName"
          language="java"
          since="3.0"
          message="It is somewhat confusing to have a field name matching the declaring class name"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidfieldnamematchingtypename">
        <description>
It is somewhat confusing to have a field name matching the declaring type name.
This probably means that type and/or field names should be chosen more carefully.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//FieldDeclaration/VariableDeclarator/VariableDeclaratorId
    [lower-case(@Name) = lower-case(ancestor::ClassOrInterfaceDeclaration[1]/@SimpleName)]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo extends Bar {
    int foo;    // There is probably a better name that can be used
}
public interface Operation {
    int OPERATION = 1; // There is probably a better name that can be used
}
]]>
        </example>
    </rule>

    <rule name="AvoidInstanceofChecksInCatchClause"
          language="java"
          since="3.0"
          message="An instanceof check is being performed on the caught exception.  Create a separate catch clause for this exception type."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidinstanceofchecksincatchclause">
        <description>
Each caught exception type should be handled in its own catch clause.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//CatchParameter
    /following-sibling::Block//InfixExpression[@Operator = 'instanceof']
        /VariableAccess[@Name = ./ancestor::Block/preceding-sibling::CatchParameter/@Name]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
try { // Avoid this
    // do something
} catch (Exception ee) {
    if (ee instanceof IOException) {
        cleanup();
    }
}

try {  // Prefer this:
    // do something
} catch (IOException ee) {
    cleanup();
}
]]>
        </example>
    </rule>

    <rule name="AvoidLiteralsInIfCondition"
          language="java"
          since="4.2.6"
          message="Avoid using literals in if statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidliteralsinifcondition">
        <description>
Avoid using hard-coded literals in conditional statements. By declaring them as static variables
or private members with descriptive names maintainability is enhanced. By default, the literals "-1" and "0" are ignored.
More exceptions can be defined with the property "ignoreMagicNumbers".

The rule doesn't consider deeper expressions by default, but this can be enabled via the property `ignoreExpressions`.
With this property set to false, if-conditions like `i == 1 + 5` are reported as well. Note that in that case,
the property ignoreMagicNumbers is not taken into account, if there are multiple literals involved in such an expression.
        </description>
        <priority>3</priority>
        <properties>
            <property name="ignoreMagicNumbers"
                      description="Comma-separated list of magic numbers, that should be ignored"
                      type="String" value="-1,0"/>
            <property name="ignoreExpressions"
                      description="If true, only literals in simple if conditions are considered. Otherwise literals in expressions are checked, too."
                      type="Boolean" value="true"/>
            <property name="xpath">
                <value>
<![CDATA[
(: simple case - no deep expressions - this is always executed :)
//IfStatement/*[1]/*[pmd-java:nodeIs('Literal')]
    [not(pmd-java:nodeIs('NullLiteral'))]
    [not(pmd-java:nodeIs('BooleanLiteral'))]
    [empty(index-of(tokenize($ignoreMagicNumbers, '\s*,\s*'), @Image))]
|
(: consider also deeper expressions :)
//IfStatement[$ignoreExpressions = false()]/*[1]//*[not(self::UnaryExpression[@Operator = '-'])]/*[pmd-java:nodeIs('Literal')]
    [not(pmd-java:nodeIs('NullLiteral'))]
    [not(pmd-java:nodeIs('BooleanLiteral'))]
    [empty(index-of(tokenize($ignoreMagicNumbers, '\s*,\s*'), @Image))]
|
(: consider negative literals :)
//IfStatement[$ignoreExpressions = false()]/*[1]//UnaryExpression[@Operator = '-']/*[pmd-java:nodeIs('Literal')]
    [not(pmd-java:nodeIs('NullLiteral'))]
    [not(pmd-java:nodeIs('BooleanLiteral'))]
    [empty(index-of(tokenize($ignoreMagicNumbers, '\s*,\s*'), concat('-', @Image)))]
|
(: consider multiple literals in expressions :)
//IfStatement[$ignoreExpressions = false()]/*[1][count(*[pmd-java:nodeIs('Literal')]
    [not(pmd-java:nodeIs('NullLiteral'))]
    [not(pmd-java:nodeIs('BooleanLiteral'))]) > 1]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
private static final int MAX_NUMBER_OF_REQUESTS = 10;

public void checkRequests() {

    if (i == 10) {                        // magic number, buried in a method
      doSomething();
    }

    if (i == MAX_NUMBER_OF_REQUESTS) {    // preferred approach
      doSomething();
    }

    if (aString.indexOf('.') != -1) {}     // magic number -1, by default ignored
    if (aString.indexOf('.') >= 0) { }     // alternative approach

    if (aDouble > 0.0) {}                  // magic number 0.0
    if (aDouble >= Double.MIN_VALUE) {}    // preferred approach

    // with rule property "ignoreExpressions" set to "false"
    if (i == pos + 5) {}  // violation: magic number 5 within an (additive) expression
    if (i == pos + SUFFIX_LENGTH) {} // preferred approach
    if (i == 5 && "none".equals(aString)) {} // 2 violations: magic number 5 and literal "none"
}
]]>
        </example>
    </rule>

    <rule name="AvoidLosingExceptionInformation"
          since="4.2.6"
          language="java"
          message="Avoid statements in a catch block that invoke accessors on the exception without using the information"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidlosingexceptioninformation">
        <description>
Statements in a catch block that invoke accessors on the exception without using the information
only add to code size.  Either remove the invocation, or use the return result.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//CatchClause/Block/ExpressionStatement/MethodCall[
    pmd-java:matchesSig("java.lang.Throwable#getMessage()")
    or pmd-java:matchesSig("java.lang.Throwable#getLocalizedMessage()")
    or pmd-java:matchesSig("java.lang.Throwable#getCause()")
    or pmd-java:matchesSig("java.lang.Throwable#getStackTrace()")
    or pmd-java:matchesSig("java.lang.Object#toString()")
]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public void bar() {
    try {
        // do something
    } catch (SomeException se) {
        se.getMessage();
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidMultipleUnaryOperators"
          language="java"
          since="4.2"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          message="Using multiple unary operators may be a bug, and/or is confusing."
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidmultipleunaryoperators">
        <description>
The use of multiple unary operators may be problematic, and/or confusing.
Ensure that the intended usage is not a bug, or consider simplifying the expression.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value><![CDATA[
                    (: Only report on the toplevel one :)
                    //UnaryExpression[UnaryExpression and not(parent::UnaryExpression)]
                ]]></value>
            </property>
        </properties>
        <example>
<![CDATA[
// These are typo bugs, or at best needlessly complex and confusing:
int i = - -1;
int j = + - +1;
int z = ~~2;
boolean b = !!true;
boolean c = !!!true;

// These are better:
int i = 1;
int j = -1;
int z = 2;
boolean b = true;
boolean c = false;

// And these just make your brain hurt:
int i = ~-2;
int j = -~7;
]]>
        </example>
    </rule>

    <rule name="AvoidUsingOctalValues"
          language="java"
          since="3.9"
          message="Do not start a literal by 0 unless it's an octal value"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidUsingOctalValuesRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidusingoctalvalues">
        <description>
Integer literals should not start with zero since this denotes that the rest of literal will be
interpreted as an octal value.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
int i = 012;    // set i with 10 not 12
int j = 010;    // set j with 8 not 10
k = i * j;      // set k with 80 not 120
]]>
        </example>
    </rule>

    <rule name="BeanMembersShouldSerialize" ref="NonSerializableClass" deprecated="true" />

    <rule name="BrokenNullCheck"
          language="java"
          since="3.8"
          message="This expression will throw a NullPointerException"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.BrokenNullCheckRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#brokennullcheck">
        <description>
The null check is broken since it will throw a NullPointerException itself.
It is likely that you used || instead of &amp;&amp; or vice versa.
        </description>
        <priority>2</priority>
        <example>
<![CDATA[
public String bar(String string) {
  // should be &&
    if (string!=null || !string.equals(""))
        return string;
  // should be ||
    if (string==null && string.equals(""))
        return string;
}
]]>
        </example>
    </rule>

    <rule name="CallSuperFirst"
          since="4.2.5"
          language="java"
          message="super should be called at the start of the method"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#callsuperfirst">
        <description>Super should be called at the start of the method</description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ClassOrInterfaceDeclaration
    [
      pmd-java:typeIs('android.app.Activity') or
      pmd-java:typeIs('android.app.Application') or
      pmd-java:typeIs('android.app.Service')
    ]
    //MethodDeclaration
    [
      @Name=('onCreate', 'onConfigurationChanged', 'onPostCreate', 'onPostResume', 'onRestart',
             'onRestoreInstanceState', 'onResume', 'onStart')
    ]
    [not(Block/*[1]/MethodCall[SuperExpression][@MethodName = ancestor::MethodDeclaration/@Name])]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
import android.app.Activity;
import android.os.Bundle;

public class DummyActivity extends Activity {
    public void onCreate(Bundle bundle) {
        // missing call to super.onCreate(bundle)
        foo();
    }
}
]]>
        </example>
    </rule>

    <rule name="CallSuperLast"
          since="4.2.5"
          language="java"
          message="super should be called at the end of the method"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#callsuperlast">
        <description>
Super should be called at the end of the method
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ClassOrInterfaceDeclaration
    [
      pmd-java:typeIs('android.app.Activity') or
      pmd-java:typeIs('android.app.Application') or
      pmd-java:typeIs('android.app.Service')
    ]
    //MethodDeclaration
    [
      @Name=('finish', 'onDestroy', 'onPause', 'onSaveInstanceState', 'onStop', 'onTerminate')
    ]
    [not(Block/*[last()]/MethodCall[SuperExpression][@MethodName = ancestor::MethodDeclaration/@Name])]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
import android.app.Activity;

public class DummyActivity extends Activity {
    public void onPause() {
        foo();
        // missing call to super.onPause()
    }
}
]]>
        </example>
    </rule>

    <rule name="CheckSkipResult"
          language="java"
          since="5.0"
          message="Check the value returned by the skip() method of an InputStream to see if the requested number of bytes has been skipped."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CheckSkipResultRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#checkskipresult">
        <description>
The skip() method may skip a smaller number of bytes than requested. Check the returned value to find out if it was the case or not.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class Foo {

   private FileInputStream _s = new FileInputStream("file");

   public void skip(int n) throws IOException {
      _s.skip(n); // You are not sure that exactly n bytes are skipped
   }

   public void skipExactly(int n) throws IOException {
      while (n != 0) {
         long skipped = _s.skip(n);
         if (skipped == 0)
            throw new EOFException();
         n -= skipped;
      }
   }
]]>
        </example>
    </rule>

    <rule name="ClassCastExceptionWithToArray"
          language="java"
          since="3.4"
          message="This usage of the Collection.toArray() method will throw a ClassCastException."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#classcastexceptionwithtoarray">
        <description>
When deriving an array of a specific class from your Collection, one should provide an array of
the same class as the parameter of the `toArray()` method. Doing otherwise will result
in a `ClassCastException`.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//CastExpression[ArrayType/ClassOrInterfaceType[not(pmd-java:typeIsExactly('java.lang.Object'))]]
    /MethodCall[pmd-java:matchesSig("java.util.Collection#toArray()")]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
Collection c = new ArrayList();
Integer obj = new Integer(1);
c.add(obj);

    // this would trigger the rule (and throw a ClassCastException if executed)
Integer[] a = (Integer [])c.toArray();

   // this is fine and will not trigger the rule
Integer[] b = (Integer [])c.toArray(new Integer[0]);
]]>
        </example>
    </rule>

    <rule name="CloneMethodMustBePublic"
          language="java"
          since="5.4.0"
          message="clone() method must be public if the class implements Cloneable"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonemethodmustbepublic">
        <description>
The java manual says "By convention, classes that implement this interface should override
Object.clone (which is protected) with a public method."
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[not(pmd-java:modifiers() = "public")]
    [@Name = 'clone']
    [@Arity = 0]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo implements Cloneable {
    @Override
    protected Object clone() throws CloneNotSupportedException { // Violation, must be public
    }
}

public class Foo implements Cloneable {
    @Override
    protected Foo clone() { // Violation, must be public
    }
}

public class Foo implements Cloneable {
    @Override
    public Object clone() // Ok
}
]]>
        </example>
    </rule>

    <rule name="CloneMethodMustImplementCloneable"
          language="java"
          since="1.9"
          message="clone() method should be implemented only if implementing Cloneable interface"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CloneMethodMustImplementCloneableRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonemethodmustimplementcloneable">
        <description>
The method clone() should only be implemented if the class implements the Cloneable interface with the exception of
a final method that only throws CloneNotSupportedException.

The rule can also detect, if the class implements or extends a Cloneable class.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class MyClass {
 public Object clone() throws CloneNotSupportedException {
  return foo;
 }
}
]]>
        </example>
    </rule>

    <rule name="CloneMethodReturnTypeMustMatchClassName"
          language="java"
          minimumLanguageVersion="1.5"
          since="5.4.0"
          message="The return type of the clone() method must be the class name when implements Cloneable"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonemethodreturntypemustmatchclassname">
        <description>
If a class implements `Cloneable` the return type of the method `clone()` must be the class name. That way, the caller
of the clone method doesn't need to cast the returned clone to the correct type.

Note: Such a covariant return type is only possible with Java 1.5 or higher.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration
    [@Name = 'clone']
    [@Arity = 0]
    [ClassOrInterfaceType[1]/@SimpleName != ancestor::ClassOrInterfaceDeclaration[1]/@SimpleName]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo implements Cloneable {
    @Override
    protected Object clone() { // Violation, Object must be Foo
    }
}

public class Foo implements Cloneable {
    @Override
    public Foo clone() { //Ok
    }
}
]]>
        </example>
    </rule>

    <rule name="CloseResource"
          language="java"
          since="1.2.2"
          message="Ensure that resources like this {0} object are closed after use"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CloseResourceRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#closeresource">
        <description>
Ensure that resources (like `java.sql.Connection`, `java.sql.Statement`, and `java.sql.ResultSet` objects
and any subtype of `java.lang.AutoCloseable`) are always closed after use.
Failing to do so might result in resource leaks.

Note: It suffices to configure the super type, e.g. `java.lang.AutoCloseable`, so that this rule automatically triggers
on any subtype (e.g. `java.io.FileInputStream`). Additionally specifying `java.sql.Connection` helps in detecting
the types, if the type resolution / auxclasspath is not correctly setup.

Note: Since PMD 6.16.0 the default value for the property `types` contains `java.lang.AutoCloseable` and detects
now cases where the standard `java.io.*Stream` classes are involved. In order to restore the old behaviour,
just remove "AutoCloseable" from the types.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class Bar {
    public void withSQL() {
        Connection c = pool.getConnection();
        try {
            // do stuff
        } catch (SQLException ex) {
           // handle exception
        } finally {
            // oops, should close the connection using 'close'!
            // c.close();
        }
    }

    public void withFile() {
        InputStream file = new FileInputStream(new File("/tmp/foo"));
        try {
            int c = file.in();
        } catch (IOException e) {
            // handle exception
        } finally {
            // TODO: close file
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="CompareObjectsWithEquals"
          language="java"
          since="3.2"
          message="Use equals() to compare object references."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#compareobjectswithequals">
        <description>
Use `equals()` to compare object references; avoid comparing them with `==`.

Since comparing objects with named constants is useful in some cases (eg, when
defining constants for sentinel values), the rule ignores comparisons against
fields with all-caps name (eg `this == SENTINEL`), which is a common naming
convention for constant fields.

You may allow some types to be compared by reference by listing the exceptions
in the `typesThatCompareByReference` property.
        </description>
        <priority>3</priority>
        <properties>
            <property name="version" value="2.0"/>
            <property name="typesThatCompareByReference" type="List[String]" delimiter="," description="List of canonical type names for which reference comparison is allowed.">
                <value>java.lang.Enum,java.lang.Class</value>
            </property>
            <property name="xpath">
                <value>
<![CDATA[
//InfixExpression
    [@Operator = ("==", "!=")]
    [count(*
        [not(self::NullLiteral)]
        [pmd-java:typeIs('java.lang.Object')]
        [not(some $t in $typesThatCompareByReference satisfies pmd-java:typeIs($t))]
      ) = 2
    ]
    [not(ancestor::MethodDeclaration[1][@Name = "equals"])]
    (: Is not a field access with an all-caps identifier :)
    [not(FieldAccess[upper-case(@Name)=@Name]
     or VariableAccess[upper-case(@Name)=@Name])]
]]>
        </value>
            </property>
        </properties>
        <example>
<![CDATA[
class Foo {
  boolean bar(String a, String b) {
    return a == b;
  }
}

]]>
        </example>
    </rule>

    <rule name="ComparisonWithNaN"
          language="java"
          since="6.36.0"
          message="Comparisons with NaN always return false"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#comparisonwithnan">
        <description><![CDATA[
            Reports comparisons with double and float `NaN` (Not-a-Number) values.
            These are [specified](https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.21.1)
            to have unintuitive behavior: NaN is considered unequal to itself.
            This means a check like `someDouble == Double.NaN` will always return
            false, even if `someDouble` is really the NaN value. To test whether a
            value is the NaN value, one should instead use `Double.isNaN(someDouble)`
            (or `Float.isNaN`). The `!=` operator should be treated similarly.
            Finally, comparisons like `someDouble <= Double.NaN` are nonsensical
            and will always evaluate to false.
            
            This rule has been renamed from "BadComparison" in PMD 6.36.0.
        ]]></description>
        <priority>3</priority>
        <properties>
            <property name="version" value="2.0"/>
            <property name="xpath">
                <value>
                    <![CDATA[
//InfixExpression[@Operator = ("==", "!=", "<=", ">=", "<", ">")]/FieldAccess[@Name='NaN' and (pmd-java:typeIs('double') or pmd-java:typeIs('float'))]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
boolean x = (y == Double.NaN);
]]>
        </example>
    </rule>


    <rule name="ConstructorCallsOverridableMethod"
          language="java"
          since="1.04"
          message="Overridable {0} called during object construction{1}"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.ConstructorCallsOverridableMethodRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod">
        <description>
Reports calls to overridable methods on `this` during object initialization. These
are invoked on an incompletely constructed object and can be difficult to debug if overridden.
This is because the subclass usually assumes that the superclass is completely initialized
in all methods. If that is not the case, bugs can appear in the constructor, for instance,
some fields that are still null may cause a NullPointerException or be stored somewhere
else to blow up later.

To avoid this problem, only use methods that are static, private, or final in constructors.
Note that those methods also must not call overridable methods transitively to be safe.
        </description>
        <priority>1</priority>
        <example>
<![CDATA[
public class SeniorClass {
  public SeniorClass(){
      toString(); //may throw NullPointerException if overridden
  }
  public String toString(){
    return "IAmSeniorClass";
  }
}
public class JuniorClass extends SeniorClass {
  private String name;
  public JuniorClass(){
    super(); //Automatic call leads to NullPointerException
    name = "JuniorClass";
  }
  public String toString(){
    return name.toUpperCase();
  }
}
]]>
        </example>
    </rule>

    <rule name="DetachedTestCase"
          language="java"
          since="6.13.0"
          message="Probable detached JUnit test case."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.DetachedTestCaseRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#detachedtestcase">
        <description>
The method appears to be a test case since it has public or default visibility,
non-static access, no arguments, no return value, has no annotations, but is a
member of a class that has one or more JUnit test cases. If it is a utility
method, it should likely have private visibility. If it is an ignored test, it
should be annotated with @Test and @Ignore.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class MyTest {
    @Test
    public void someTest() {
    }

    // violation: Not annotated
    public void someOtherTest () {
    }

}
]]>
        </example>
    </rule>

    <rule name="DoNotCallGarbageCollectionExplicitly"
          language="java"
          since="4.2"
          message="Do not explicitly trigger a garbage collection."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotcallgarbagecollectionexplicitly">
        <description>
Calls to `System.gc()`, `Runtime.getRuntime().gc()`, and `System.runFinalization()` are not advised.
Code should have the same behavior whether the garbage collection is disabled using the option
`-Xdisableexplicitgc` or not.

Moreover, "modern" JVMs do a very good job handling garbage collections. If memory usage issues unrelated to memory
leaks develop within an application, it should be dealt with JVM options rather than within the code itself.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall[
       pmd-java:matchesSig("java.lang.System#gc()")
    or pmd-java:matchesSig("java.lang.Runtime#gc()")
    or pmd-java:matchesSig("java.lang.System#runFinalization()")
    or pmd-java:matchesSig("java.lang.Runtime#runFinalization()")
]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class GCCall {
    public GCCall() {
        // Explicit gc call !
        System.gc();
    }

    public void doSomething() {
        // Explicit gc call !
        Runtime.getRuntime().gc();
    }

    public explicitGCcall() {
        // Explicit gc call !
        System.gc();
    }

    public void doSomething() {
        // Explicit gc call !
        Runtime.getRuntime().gc();
    }
}
]]>
        </example>
    </rule>

    <rule name="DoNotExtendJavaLangThrowable"
          language="java"
          since="6.0.0"
          message="Exceptions should not extend java.lang.Throwable"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotextendjavalangthrowable">
        <description>
Extend Exception or RuntimeException instead of Throwable.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ClassOrInterfaceDeclaration/ExtendsList/ClassOrInterfaceType
  [pmd-java:typeIsExactly('java.lang.Throwable')]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo extends Throwable { }
]]>
        </example>
    </rule>

    <rule name="DoNotHardCodeSDCard"
          since="4.2.6"
          language="java"
          message="Do not hardcode /sdcard."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donothardcodesdcard">
        <description>
Use Environment.getExternalStorageDirectory() instead of "/sdcard"
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//StringLiteral[starts-with(@Image,'"/sdcard')]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class MyActivity extends Activity {
    protected void foo() {
        String storageLocation = "/sdcard/mypackage";   // hard-coded, poor approach

       storageLocation = Environment.getExternalStorageDirectory() + "/mypackage"; // preferred approach
    }
}
]]>
        </example>
    </rule>

    <rule name="DoNotTerminateVM"
          language="java"
          since="4.1"
          message="System.exit() should not be used in J2EE/JEE apps"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotterminatevm">
        <description>
Web applications should not call `System.exit()`, since only the web container or the
application server should stop the JVM. Otherwise a web application would terminate all other applications
running on the same application server.

This rule also checks for the equivalent calls `Runtime.getRuntime().exit()` and `Runtime.getRuntime().halt()`.

This rule has been renamed from "DoNotCallSystemExit" in PMD 6.29.0.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//(MethodDeclaration[@MainMethod = false()] | Initializer)//MethodCall[
    pmd-java:matchesSig("java.lang.System#exit(int)")
    or pmd-java:matchesSig("java.lang.Runtime#exit(int)")
    or pmd-java:matchesSig("java.lang.Runtime#halt(int)")
]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public void bar() {
    System.exit(0);                 // never call this when running in an application server!
}
public void foo() {
    Runtime.getRuntime().exit(0);   // never stop the JVM manually, the container will do this.
}
]]>
        </example>
    </rule>

    <rule name="DoNotThrowExceptionInFinally"
          language="java"
          since="4.2"
          message="A throw statement in a finally block makes the control flow hard to understand."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotthrowexceptioninfinally">
        <description>
Throwing exceptions within a 'finally' block is confusing since they may mask other exceptions
or code defects.
Note: This is a PMD implementation of the Lint4j rule "A throw in a finally block"
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>//FinallyClause[descendant::ThrowStatement]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    public void bar() {
        try {
            // Here do some stuff
        } catch( Exception e) {
            // Handling the issue
        } finally {
            // is this really a good idea ?
            throw new Exception();
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="DontImportSun"
          language="java"
          since="1.5"
          message="Avoid importing anything from the 'sun.*' packages"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#dontimportsun">
        <description>
Avoid importing anything from the 'sun.*' packages. These packages are not portable
and are likely to change.

If you find yourself having to depend on Sun APIs, confine this dependency to as
small a scope as possible, for instance by writing a stable wrapper class around
the unstable API. You can then suppress this rule in the implementation of the wrapper.
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ImportDeclaration[starts-with(@ImportedName, 'sun.')]
]]>
                </value>
            </property>

        </properties>
        <example>
<![CDATA[
import sun.misc.foo;
public class Foo {}
]]>
        </example>
    </rule>

    <rule name="DontUseFloatTypeForLoopIndices"
          language="java"
          since="4.3"
          message="Don't use floating point for loop indices. If you must use floating point, use double."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#dontusefloattypeforloopindices">
        <description>
Don't use floating point for loop indices. If you must use floating point, use double
unless you're certain that float provides enough precision and you have a compelling
performance need (space or time).
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ForStatement/ForInit//VariableDeclaratorId[pmd-java:typeIs('float')]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Count {
  public static void main(String[] args) {
    final int START = 2000000000;
    int count = 0;
    for (float f = START; f < START + 50; f++)
      count++;
      //Prints 0 because (float) START == (float) (START + 50).
      System.out.println(count);
      //The termination test misbehaves due to floating point granularity.
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyCatchBlock"
          language="java"
          since="0.1"
          message="Avoid empty catch blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptycatchblock">
        <description>
Empty Catch Block finds instances where an exception is caught, but nothing is done.
In most circumstances, this swallows an exception which should either be acted on
or reported.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//CatchClause[
  Block[
      count(*) = 0
      and ($allowCommentedBlocks = false() or Block/@containsComment = false())
  ]
  and CatchParameter/VariableDeclaratorId[not(matches(@Name, $allowExceptionNameRegex))]
]
]]>
                </value>
            </property>
            <property name="allowCommentedBlocks" type="Boolean" description="Empty blocks containing comments will be skipped" value="false"/>
            <property name="allowExceptionNameRegex" type="String" description="Empty blocks catching exceptions with names matching this regular expression will be skipped" value="^(ignored|expected)$"/>
        </properties>
        <example>
<![CDATA[
public void doSomething() {
    try {
        FileInputStream fis = new FileInputStream("/tmp/bugger");
    } catch (IOException ioe) {
        // not good
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyFinalizer"
          language="java"
          since="1.5"
          message="Avoid empty finalize methods"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyfinalizer">
        <description>
Empty finalize methods serve no purpose and should be removed. Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[@Name='finalize'][@Arity = 0]
  /Block[not(*)]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
   protected void finalize() {}
}
]]>
        </example>
    </rule>

    <rule name="EmptyFinallyBlock"
          deprecated="true"
          language="java"
          since="0.4"
          message="Avoid empty finally blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyfinallyblock">
        <description>
Empty finally blocks serve no purpose and should be removed.

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//FinallyClause[Block[not(*)]]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    public void bar() {
        try {
            int x=2;
        } finally {
            // empty!
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyIfStmt"
          deprecated="true"
          language="java"
          since="0.1"
          message="Avoid empty 'if' statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyifstmt">
        <description>
Empty If Statement finds instances where a condition is checked but nothing is done about it.

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//IfStatement/*[self::EmptyStatement or self::Block[not(*)]]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
 void bar(int x) {
  if (x == 0) {
   // empty!
  }
 }
}
]]>
        </example>
    </rule>

    <rule name="EmptyInitializer"
          deprecated="true"
          language="java"
          since="5.0"
          message="Empty initializer was found"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyinitializer">
        <description>
Empty initializers serve no purpose and should be removed.

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//Initializer/Block[not(*)]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {

   static {} // Why ?

   {} // Again, why ?

}
]]>
        </example>
    </rule>

    <rule name="EmptyStatementBlock"
          deprecated="true"
          language="java"
          since="5.0"
          message="Avoid empty block statements."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptystatementblock">
        <description>
Empty block statements serve no purpose and should be removed.

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//Block[not(*)][parent::Block or parent::SwitchFallthroughBranch or parent::SwitchArrowBranch]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {

   private int _bar;

   public void setBar(int bar) {
      { _bar = bar; } // Why not?
      {} // But remove this.
   }

}
]]>
        </example>
    </rule>

    <rule name="EmptyStatementNotInLoop"
          language="java"
          since="1.5"
          deprecated="true"
          message="An empty statement (semicolon) not part of a loop"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptystatementnotinloop">
        <description>
An empty statement (or a semicolon by itself) that is not used as the sole body of a 'for'
or 'while' loop is probably a bug.  It could also be a double semicolon, which has no purpose
and should be removed.

_Note:_ This rule is deprecated since PMD 6.53.0 and will be removed with PMD 7.0.0.
Use the rule {% rule java/codestyle/UnnecessarySemicolon %} instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//EmptyStatement
 [not(
          parent::WhileStatement
       or parent::ForStatement
       or parent::ForeachStatement
       or preceding-sibling::*[1]/self::LocalClassStatement
  )
 ]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public void doit() {
      // this is probably not what you meant to do
      ;
      // the extra semicolon here this is not necessary
      System.out.println("look at the extra semicolon");;
}
]]>
        </example>
    </rule>

    <rule name="EmptySwitchStatements"
          deprecated="true"
          language="java"
          since="1.0"
          message="Avoid empty switch statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyswitchstatements">
        <description>
Empty switch statements serve no purpose and should be removed.#

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//SwitchStatement[count(*) = 1]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public void bar() {
    int x = 2;
    switch (x) {
        // once there was code here
        // but it's been commented out or something
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptySynchronizedBlock"
          deprecated="true"
          language="java"
          since="1.3"
          message="Avoid empty synchronized blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptysynchronizedblock">
        <description>
Empty synchronized blocks serve no purpose and should be removed.

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//SynchronizedStatement/Block[not(*)]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    public void bar() {
        synchronized (this) {
            // empty!
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyTryBlock"
          deprecated="true"
          language="java"
          since="0.4"
          message="Avoid empty try blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptytryblock">
        <description>
Avoid empty try blocks - what's the point?

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//TryStatement[not(ResourceList)]/Block[not(*)]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    public void bar() {
        try {
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyWhileStmt"
          deprecated="true"
          language="java"
          since="0.2"
          message="Avoid empty 'while' statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptywhilestmt">
        <description>
Empty While Statement finds all instances where a while statement does nothing.
If it is a timing loop, then you should use Thread.sleep() for it; if it is
a while loop that does a lot in the exit expression, rewrite it to make it clearer.

_Note:_ This rule is deprecated since PMD 6.46.0 and will be removed with PMD 7.0.0.
Use the rule {% rule "java/codestyle/EmptyControlStatement" %} from category codestyle instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//WhileStatement/*[self::Block[not(*)] or self::EmptyStatement]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
void bar(int a, int b) {
    while (a == b) {
        // empty!
    }
}
 ]]>
        </example>
    </rule>

    <rule name="EqualsNull"
          language="java"
          since="1.9"
          message="Avoid using equals() to compare against null"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#equalsnull">
        <description>
Tests for null should not use the equals() method. The '==' operator should be used instead.
        </description>
        <priority>1</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall[@MethodName = "equals" and ArgumentList[count(*) = 1 and NullLiteral]]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
String x = "foo";

if (x.equals(null)) {   // bad form
    doSomething();
}

if (x == null) {        // preferred
    doSomething();
}
]]>
        </example>
    </rule>

    <rule name="FinalizeDoesNotCallSuperFinalize"
          language="java"
          since="1.5"
          message="Last statement in finalize method should be a call to super.finalize()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizedoesnotcallsuperfinalize">
        <description>
If the finalize() is implemented, its last action should be to call super.finalize. Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<!-- in English: a method declaration of finalize(), with no arguments, containing
a block whose last statement is NOT a call to super.finalize -->
<![CDATA[
//MethodDeclaration[@Name = "finalize"][@Arity = 0]
   /Block/*[last()]
      [not(MethodCall[@MethodName = "finalize"]/SuperExpression)]
      [not(FinallyClause/Block/ExpressionStatement/
          MethodCall[@MethodName = "finalize"]/SuperExpression)]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
protected void finalize() {
    something();
    // neglected to call super.finalize()
}
]]>
        </example>
    </rule>

    <rule name="FinalizeOnlyCallsSuperFinalize"
          language="java"
          since="1.5"
          message="Finalize should do something besides just calling super.finalize()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizeonlycallssuperfinalize">
        <description>
If the finalize() is implemented, it should do something besides just calling super.finalize(). Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[@Name='finalize'][@Arity = 0]
   [Block[@Size=1]/ExpressionStatement/MethodCall[@MethodName = "finalize"][SuperExpression]]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
protected void finalize() {
    super.finalize();
}
]]>
        </example>
    </rule>

    <rule name="FinalizeOverloaded"
          language="java"
          since="1.5"
          message="Finalize methods should not be overloaded"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizeoverloaded">
        <description>
Methods named finalize() should not have parameters.  It is confusing and most likely an attempt to
overload Object.finalize(). It will not be called by the VM.

Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[@Name='finalize'][@Arity > 0]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    // this is confusing and probably a bug
    protected void finalize(int a) {
    }
}
]]>
        </example>
    </rule>

    <rule name="FinalizeShouldBeProtected"
          language="java"
          since="1.1"
          message="If you override finalize(), make it protected"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizeshouldbeprotected">
        <description>
When overriding the finalize(), the new method should be set as protected.  If made public,
other classes may invoke it at inappropriate times.

Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[@Visibility != "protected"][@Name='finalize'][@Arity = 0]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public void finalize() {
    // do something
}
]]>
        </example>
    </rule>

    <rule name="IdempotentOperations"
          language="java"
          since="2.0"
          message="Avoid idempotent operations (like assigning a variable to itself)."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.IdempotentOperationsRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#idempotentoperations">
        <description>
Avoid idempotent operations - they have no effect.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class Foo {
 public void bar() {
  int x = 2;
  x = x;
 }
}
]]>
        </example>
    </rule>

    <rule name="ImplicitSwitchFallThrough"
          language="java"
          since="3.0"
          message="This switch case may be reached by fallthrough from the previous case"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.ImplicitSwitchFallThroughRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#implicitswitchfallthrough">
        <description>
Switch statements without break or return statements for each case option
may indicate problematic behaviour. Empty cases are ignored as these indicate
an intentional fall-through.

You can ignore a violation by commenting `// fallthrough` before the case label
which is reached by fallthrough, or with `@SuppressWarnings("fallthrough")`.

This rule has been renamed from "MissingBreakInSwitch" in PMD 6.37.0.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public void bar(int status) {
    switch(status) {
      case CANCELLED:
        doCancelled();
        // break; hm, should this be commented out?
      case NEW:
        doNew();
        // is this really a fall-through?
        // what happens if you add another case after this one?
      case REMOVED:
        doRemoved();
        // fallthrough - this comment just clarifies that you want a fallthrough
      case OTHER: // empty case - this is interpreted as an intentional fall-through
      case ERROR:
        doErrorHandling();
        break;
    }
}
]]>
        </example>
    </rule>

    <rule name="InstantiationToGetClass"
          language="java"
          since="2.0"
          message="Avoid instantiating an object just to call getClass() on it; use the .class public member instead"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#instantiationtogetclass">
        <description>
Avoid instantiating an object just to call getClass() on it; use the .class public member instead.
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall
 [@MethodName='getClass']
 [ConstructorCall]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
// replace this
Class c = new String().getClass();

// with this:
Class c = String.class;
]]>
        </example>
    </rule>

    <rule name="InvalidLogMessageFormat"
          language="java"
          since="5.5.0"
          message="Invalid message format"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.InvalidLogMessageFormatRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#invalidlogmessageformat">
        <description>
Check for messages in slf4j and log4j2 (since 6.19.0) loggers with non matching number of arguments and placeholders.

Since 6.32.0 in addition to parameterized message placeholders (`{}`) also format specifiers of string formatted
messages are supported (`%s`).

This rule has been renamed from "InvalidSlf4jMessageFormat" in PMD 6.19.0.
        </description>
        <priority>5</priority>
        <example>
<![CDATA[
LOGGER.error("forget the arg {}");
LOGGER.error("forget the arg %s");
LOGGER.error("too many args {}", "arg1", "arg2");
LOGGER.error("param {}", "arg1", new IllegalStateException("arg")); //The exception is shown separately, so is correct.
]]>
        </example>
    </rule>

    <rule name="JumbledIncrementer"
          language="java"
          since="1.0"
          message="Avoid modifying an outer loop incrementer in an inner loop for update expression"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#jumbledincrementer">
        <description>
Avoid jumbled loop incrementers - it's usually a mistake, and is confusing even if intentional.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value><![CDATA[
//ForStatement
    [not(ForInit) or ForInit//VariableDeclaratorId/@Name != ForUpdate//VariableAccess/@Name]
    [ForUpdate//VariableAccess[@AccessType = 'WRITE']/@Name
     =
     ancestor::ForStatement/ForInit//VariableDeclaratorId/@Name
    ]
]]>
                </value>
            </property>
        </properties>
        <example>
 <![CDATA[
public class JumbledIncrementerRule1 {
    public void foo() {
        for (int i = 0; i < 10; i++) {          // only references 'i'
            for (int k = 0; k < 20; i++) {      // references both 'i' and 'k'
                System.out.println("Hello");
            }
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="JUnitSpelling"
          language="java"
          since="1.0"
          message="You may have misspelled a JUnit framework method (setUp or tearDown)"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.JUnitSpellingRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#junitspelling">
        <description>
            In JUnit 3, the setUp method is used to set up all data entities required in running tests.
            The tearDown method is used to clean up all data entities required in running tests.
            You should not misspell method name if you want your test to set up and clean up everything correctly.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
import junit.framework.*;

public class Foo extends TestCase {
    public void setup() {}    // oops, should be setUp
    public void TearDown() {} // oops, should be tearDown
}
]]>
        </example>
    </rule>

    <rule name="JUnitStaticSuite"
          language="java"
          since="1.0"
          message="You have a suite() method that is not both public and static, so JUnit won't call it to get your TestSuite.  Is that what you wanted to do?"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.JUnitStaticSuiteRule"
          typeResolution="true"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#junitstaticsuite">
        <description>
The suite() method in a JUnit test needs to be both public and static.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
import junit.framework.*;

public class Foo extends TestCase {
    public void suite() {}         // oops, should be static
    private static void suite() {} // oops, should be public
}
]]>
        </example>
    </rule>

    <rule name="MethodWithSameNameAsEnclosingClass"
          language="java"
          since="1.5"
          message="A method should not have the same name as its containing class"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#methodwithsamenameasenclosingclass">
        <description>
A method should not have the same name as its containing class.
This would be confusing as it would look like a constructor. 
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[@Name = ancestor::ClassOrInterfaceDeclaration/@SimpleName]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class MyClass {

    public MyClass() {}         // this is OK because it is a constructor

    public void MyClass() {}    // this is bad because it is a method
}
]]>
        </example>
    </rule>

    <rule name="MisplacedNullCheck"
          language="java"
          since="3.5"
          message="The null check here is misplaced; if the variable ''{0}'' is null there will be a NullPointerException"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#misplacednullcheck">
        <description>
The null check here is misplaced. If the variable is null a `NullPointerException` will be thrown.
Either the check is useless (the variable will never be `null`) or it is incorrect.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//InfixExpression[@Operator = '&&']
    /InfixExpression[@Operator = '!=']
        (: one side is null :)
        [NullLiteral]
        (: other side checks for the variable used somewhere in the first child of conditional and expression :)
        [VariableAccess]
        [some $var in preceding-sibling::*//VariableAccess
            [parent::MethodCall or parent::FieldAccess]
            [not(ancestor::InfixExpression[@Operator = '||'])]
            /@Name
            satisfies $var = VariableAccess/@Name
        ]
    /VariableAccess
|
//InfixExpression[@Operator = '||']
    /InfixExpression[@Operator = '==']
        (: one side is null :)
        [NullLiteral]
        (: other side checks for the variable used somewhere in the first child of conditional or expression :)
        [VariableAccess]
        [some $var in preceding-sibling::*//VariableAccess
            [parent::MethodCall or parent::FieldAccess]
            [not(ancestor::InfixExpression[@Operator = '&&'])]
            /@Name
            satisfies $var = VariableAccess/@Name
        ]
    /VariableAccess
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    void bar() {
        if (a.equals(baz) && a != null) {} // a could be null, misplaced null check

        if (a != null && a.equals(baz)) {} // correct null check
    }
}
]]>
        </example>
        <example>
<![CDATA[
public class Foo {
    void bar() {
        if (a.equals(baz) || a == null) {} // a could be null, misplaced null check

        if (a == null || a.equals(baz)) {} // correct null check
    }
}
]]>
        </example>
    </rule>

    <rule name="MissingSerialVersionUID"
          language="java"
          since="3.0"
          message="Classes implementing Serializable should set a serialVersionUID"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#missingserialversionuid">
        <description>
Serializable classes should provide a serialVersionUID field.
The serialVersionUID field is also needed for abstract base classes. Each individual class in the inheritance
chain needs an own serialVersionUID field. See also [Should an abstract class have a serialVersionUID](https://stackoverflow.com/questions/893259/should-an-abstract-class-have-a-serialversionuid).
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ClassOrInterfaceDeclaration
    [@Interface = false()]
    [count(ClassOrInterfaceBody/FieldDeclaration/VariableDeclarator/VariableDeclaratorId[@Name='serialVersionUID']) = 0]
    [(ImplementsList | ExtendsList)/ClassOrInterfaceType[pmd-java:typeIs('java.io.Serializable')]]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo implements java.io.Serializable {
    String name;
    // Define serialization id to avoid serialization related bugs
    // i.e., public static final long serialVersionUID = 4328743;
}
]]>
        </example>
    </rule>

    <rule name="MissingStaticMethodInNonInstantiatableClass"
          language="java"
          since="3.0"
          message="Class cannot be instantiated and does not provide any static methods or fields"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#missingstaticmethodinnoninstantiatableclass">
        <description>
A class that has private constructors and does not have any static methods or fields cannot be used.

When one of the private constructors is annotated with one of the annotations, then the class is not considered
non-instantiatable anymore and no violation will be reported.
See the property `annotations`.
        </description>
        <priority>3</priority>
        <properties>
            <property name="annotations" type="List[String]" delimiter="," value="org.springframework.beans.factory.annotation.Autowired,javax.inject.Inject,com.google.inject.Inject" description="If a constructor is annotated with one of these annotations, then the class is ignored."/>
            <property name="xpath">
                <value>
<![CDATA[
let $topLevelClass := /*/ClassOrInterfaceDeclaration return
let $isLombokUtility := exists($topLevelClass[pmd-java:hasAnnotation('lombok.experimental.UtilityClass')]) return
$topLevelClass[
        (: non-instantiable :)
        $isLombokUtility or
        (
            (: no lombok produced constructors :)
            not(pmd-java:hasAnnotation('lombok.NoArgsConstructor') or
                pmd-java:hasAnnotation('lombok.RequiredArgsConstructor') or
                pmd-java:hasAnnotation('lombok.AllArgsConstructor')) and
            (: or has non-default constructors … :)
            ClassOrInterfaceBody/ConstructorDeclaration and
                (: … but only private … :)
                not(ClassOrInterfaceBody/ConstructorDeclaration[@Visibility != "private"]) and
                (: … and none annotated … :)
                (every $x in $annotations satisfies
                      not(ClassOrInterfaceBody/ConstructorDeclaration/ModifierList/Annotation[pmd-java:typeIs($x)]))
        )
    ]
    [
        (: With no visible static methods … :)
        not(ClassOrInterfaceBody/MethodDeclaration[($isLombokUtility or pmd-java:modifiers() = "static") and @Visibility != "private"]) and
        (: … nor fields … :)
        not(ClassOrInterfaceBody/FieldDeclaration[($isLombokUtility or pmd-java:modifiers() = "static") and @Visibility != "private"]) and
        (: … no nested classes, that are non-private and static … :)
        not(ClassOrInterfaceBody/ClassOrInterfaceDeclaration
            [pmd-java:modifiers() = "static" and @Visibility != "private"]
            (: … with a default or non-private constructor … :)
            [not(ClassOrInterfaceBody/ConstructorDeclaration) or ClassOrInterfaceBody/ConstructorDeclaration[@Visibility != "private"]]
            (: … and a non-private method returning the outer class type … :)
            [(ClassOrInterfaceBody/MethodDeclaration
                [@Visibility != "private"]
                [descendant::ReturnStatement/*[1][pmd-java:typeIs(ancestor::ClassOrInterfaceDeclaration[@Nested = false()]/@BinaryName)]]
            ) or (
                (: … or the inner class extends the outer class :)
                ExtendsList/ClassOrInterfaceType[@SimpleName = ancestor::ClassOrInterfaceDeclaration[@Nested = false()]/@SimpleName]
            )]
    )]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
// This class is unusable, since it cannot be
// instantiated (private constructor),
// and no static method can be called.

public class Foo {
  private Foo() {}
  void foo() {}
}

]]>
        </example>
    </rule>

    <rule name="MoreThanOneLogger"
          language="java"
          since="2.0"
          message="Class contains more than one logger."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#morethanonelogger">
        <description>
Normally only one logger is used in each class. This rule supports slf4j, log4j, Java Util Logging and
log4j2 (since 6.19.0).
        </description>
        <priority>2</priority>
        <properties>
            <property name="version" value="2.0"/>
            <property name="xpath">
                <value><![CDATA[
//ClassOrInterfaceDeclaration[
  count(
    ClassOrInterfaceBody/FieldDeclaration/ClassOrInterfaceType[
      pmd-java:typeIs("org.apache.log4j.Logger") or
      pmd-java:typeIs("org.apache.logging.log4j.Logger") or
      pmd-java:typeIs("java.util.logging.Logger") or
      pmd-java:typeIs("org.slf4j.Logger")
    ]
  ) > 1
]
                ]]></value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    Logger log = Logger.getLogger(Foo.class.getName());
    // It is very rare to see two loggers on a class, normally
    // log information is multiplexed by levels
    Logger log2= Logger.getLogger(Foo.class.getName());
}
]]>
        </example>
    </rule>

    <rule name="NonCaseLabelInSwitchStatement"
          language="java"
          since="1.5"
          message="A non-case label was present in a switch statement"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#noncaselabelinswitchstatement">
        <description>
A non-case label (e.g. a named break/continue label) was present in a switch statement.
This is legal, but confusing. It is easy to mix up the case labels and the non-case labels.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//SwitchStatement//LabeledStatement</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
  void bar(int a) {
   switch (a) {
     case 1:
       // do something
       break;
     mylabel: // this is legal, but confusing!
       break;
     default:
       break;
    }
  }
}
]]>
        </example>
    </rule>

    <rule name="NonSerializableClass"
          language="java"
          since="1.1"
          message="The field ''{0}'' of serializable class ''{1}'' is of non-serializable type ''{2}''."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.NonSerializableClassRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#nonserializableclass">
        <description>
If a class is marked as `Serializable`, then all fields need to be serializable as well. In order to exclude
a field, it can be marked as transient. Static fields are not considered.

This rule reports all fields, that are not serializable.

If a class implements the methods to perform manual serialization (`writeObject`, `readObject`) or uses
a replacement object (`writeReplace`, `readResolve`) then this class is ignored.

Note: This rule has been revamped with PMD 6.52.0. It was previously called "BeanMembersShouldSerialize".
The property `prefix` has been deprecated, since in a serializable class all fields have to be
serializable regardless of the name.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
class Buzz implements java.io.Serializable {
    private static final long serialVersionUID = 1L;

    private transient int someFoo;          // good, it's transient
    private static int otherFoo;            // also OK, it's static
    private java.io.FileInputStream stream; // bad - FileInputStream is not serializable

    public void setStream(FileInputStream stream) {
        this.stream = stream;
    }

    public int getSomeFoo() {
          return this.someFoo;
    }
}
]]>
        </example>
    </rule>

    <rule name="NonStaticInitializer"
          language="java"
          since="1.5"
          message="Non-static initializers are confusing"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#nonstaticinitializer">
        <description>
A non-static initializer block will be called any time a constructor is invoked (just prior to
invoking the constructor).  While this is a valid language construct, it is rarely used and is
confusing.
        </description>
        <priority>3</priority>
        <properties>
            <property name="version" value="2.0" />
            <property name="xpath">
                <value>
<![CDATA[
//Initializer[@Static=false()][not(ancestor::*[3][self::ConstructorCall or self::EnumConstant])]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class MyClass {
  // this block gets run before any call to a constructor
  {
    System.out.println("I am about to construct myself");
  }
}
]]>
        </example>
    </rule>

    <rule name="NullAssignment"
          language="java"
          since="1.02"
          message="Assigning an Object to null is a code smell.  Consider refactoring."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.NullAssignmentRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#nullassignment">
        <description>
Assigning a "null" to a variable (outside of its declaration) is usually bad form.  Sometimes, this type
of assignment is an indication that the programmer doesn't completely understand what is going on in the code.

NOTE: This sort of assignment may used in some cases to dereference objects and encourage garbage collection.
        </description>
        <priority>3</priority>
        <example>
 <![CDATA[
public void bar() {
  Object x = null; // this is OK
  x = new Object();
     // big, complex piece of code here
  x = null; // this is not required
     // big, complex piece of code here
}
]]>
        </example>
    </rule>

    <rule name="OverrideBothEqualsAndHashcode"
          language="java"
          since="0.4"
          message="Ensure you override both equals() and hashCode()"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.OverrideBothEqualsAndHashcodeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#overridebothequalsandhashcode">
        <description>
Override both public boolean Object.equals(Object other), and public int Object.hashCode(), or override neither.  Even if you are inheriting a hashCode() from a parent class, consider implementing hashCode and explicitly delegating to your superclass.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public class Bar {        // poor, missing a hashcode() method
    public boolean equals(Object o) {
      // do some comparison
    }
}

public class Baz {        // poor, missing an equals() method
    public int hashCode() {
      // return some hash value
    }
}

public class Foo {        // perfect, both methods provided
    public boolean equals(Object other) {
      // do some comparison
    }
    public int hashCode() {
      // return some hash value
    }
}
]]>
        </example>
    </rule>

    <rule name="ProperCloneImplementation"
          language="java"
          since="1.4"
          message="Object clone() should be implemented with super.clone()"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.ProperCloneImplementationRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#propercloneimplementation">
        <description>
Object clone() should be implemented with super.clone().
        </description>
        <priority>2</priority>
        <example>
<![CDATA[
class Foo{
    public Object clone(){
        return new Foo(); // This is bad
    }
}
]]>
        </example>
    </rule>

    <rule name="ProperLogger"
          language="java"
          since="3.3"
          message="Logger should be defined private static final and have the correct class"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#properlogger">
        <description>
A logger should normally be defined private static final and be associated with the correct class.
`private final Log log;` is also allowed for rare cases where loggers need to be passed around,
with the restriction that the logger needs to be passed into the constructor.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//FieldDeclaration
    [ClassOrInterfaceType[pmd-java:typeIs($loggerClass)]]
    [
        (: check modifiers :)
        (not(pmd-java:modifiers() = 'private') or not(pmd-java:modifiers() = 'final'))
        (: check logger name :)
        or (pmd-java:modifiers() = 'static' and VariableDeclarator/VariableDeclaratorId/@Name != $staticLoggerName)
        or (not(pmd-java:modifiers() = 'static') and VariableDeclarator/VariableDeclaratorId/@Name != $loggerName)
        (: check logger argument type matches class or enum name :)
        or .//ArgumentList/ClassLiteral/ClassOrInterfaceType/@SimpleName != ancestor::ClassOrInterfaceDeclaration/@SimpleName
        or .//ArgumentList/ClassLiteral/ClassOrInterfaceType/@SimpleName != ancestor::EnumDeclaration/@SimpleName

        (: special case - final logger initialized inside constructor :)
        or (VariableDeclarator/@Initializer = false()
            and not(pmd-java:modifiers() = 'static')
            and not(ancestor::ClassOrInterfaceBody/ConstructorDeclaration
                //AssignmentExpression[@Operator = '=']
                    [FieldAccess[1]/@Name = $loggerName or VariableAccess[1]/@Name = $loggerName]
                    [*[2][@Name = ancestor::ConstructorDeclaration//FormalParameter/VariableDeclaratorId/@Name]])
        )
    ]
]]>
                </value>
            </property>
            <property name="staticLoggerName" type="String" description="Name of the static Logger variable" value="LOG"/>
            <property name="loggerName" type="String" description="Name of the Logger instance variable" value="log"/>
            <property name="loggerClass" type="String" description="Class name of the logger" value="org.apache.commons.logging.Log"/>
        </properties>
        <example>
 <![CDATA[
public class Foo {

    private static final Log LOG = LogFactory.getLog(Foo.class);    // proper way

    protected Log LOG = LogFactory.getLog(Testclass.class);         // wrong approach
}
]]>
        </example>
    </rule>

    <rule name="ReturnEmptyCollectionRatherThanNull"
          language="java"
          since="6.37.0"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          message="Return an empty collection rather than 'null'."
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull">
        <description>
For any method that returns an collection (such as an array, Collection or Map), it is better to return
an empty one rather than a null reference. This removes the need for null checking all results and avoids
inadvertent NullPointerExceptions.

See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null
        </description>
        <priority>1</priority>
        <properties>
            <property name="version" value="2.0"/>
            <property name="xpath">
                <value>
<![CDATA[
//ReturnStatement/NullLiteral
[ancestor::MethodDeclaration[1]
    [ArrayType
     or ClassOrInterfaceType[pmd-java:typeIs('java.util.Collection')
        or pmd-java:typeIs('java.util.Map')]]
]
[not(./ancestor::LambdaExpression)]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Example {
    // Not a good idea...
    public int[] badBehavior() {
        // ...
        return null;
    }

    // Good behavior
    public String[] bonnePratique() {
        //...
        return new String[0];
    }
}
]]>
        </example>
    </rule>

    <rule name="ReturnFromFinallyBlock"
          language="java"
          since="1.05"
          message="Avoid returning from a finally block"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#returnfromfinallyblock">
        <description>
Avoid returning from a finally block, this can discard exceptions.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//FinallyClause//ReturnStatement except //FinallyClause//(MethodDeclaration|LambdaExpression)//ReturnStatement</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Bar {
    public String foo() {
        try {
            throw new Exception( "My Exception" );
        } catch (Exception e) {
            throw e;
        } finally {
            return "A. O. K."; // return not recommended here
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="SimpleDateFormatNeedsLocale"
          language="java"
          since="2.0"
          message="When instantiating a SimpleDateFormat object, specify a Locale"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#simpledateformatneedslocale">
        <description>
Be sure to specify a Locale when creating SimpleDateFormat instances to ensure that locale-appropriate
formatting is used.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ConstructorCall
    [pmd-java:typeIs('java.text.SimpleDateFormat')]
    [ArgumentList/@Size = 1]
]]>
                    </value>
                </property>
            </properties>
        <example>
<![CDATA[
public class Foo {
  // Should specify Locale.US (or whatever)
  private SimpleDateFormat sdf = new SimpleDateFormat("pattern");
}
]]>
        </example>
    </rule>

    <rule name="SingleMethodSingleton"
          language="java"
          since="5.4"
          message="Class contains multiple getInstance methods. Please review."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SingleMethodSingletonRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#singlemethodsingleton">
        <description>
Some classes contain overloaded getInstance. The problem with overloaded getInstance methods
is that the instance created using the overloaded method is not cached and so,
for each call and new objects will be created for every invocation.
        </description>
        <priority>2</priority>
        <example>
<![CDATA[
public class Singleton {

    private static Singleton singleton = new Singleton( );

    private Singleton(){ }

    public static Singleton getInstance( ) {
        return singleton;
    }

    public static Singleton getInstance(Object obj){
        Singleton singleton = (Singleton) obj;
        return singleton;           //violation
    }
}
]]>
        </example>
    </rule>

    <rule name="SingletonClassReturningNewInstance"
          language="java"
          since="5.4"
          message="getInstance method always creates a new object and hence does not comply to Singleton Design Pattern behaviour. Please review"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SingletonClassReturningNewInstanceRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#singletonclassreturningnewinstance">
        <description>
            A singleton class should only ever have one instance. Failure to check
            whether an instance has already been created may result in multiple
            instances being created.
        </description>
        <priority>2</priority>
        <example>
<![CDATA[
class Singleton {
    private static Singleton instance = null;
    public static Singleton getInstance() {
        synchronized(Singleton.class) {
            return new Singleton(); // this should be assigned to the field
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="StaticEJBFieldShouldBeFinal"
          language="java"
          since="4.1"
          message="EJB's shouldn't have non-final static fields"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#staticejbfieldshouldbefinal">
        <description>
According to the J2EE specification, an EJB should not have any static fields
with write access. However, static read-only fields are allowed. This ensures proper
behavior especially when instances are distributed by the container on several JREs.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ClassOrInterfaceDeclaration[ImplementsList/ClassOrInterfaceType[
        pmd-java:typeIs('javax.ejb.SessionBean')
     or pmd-java:typeIs('javax.ejb.EJBHome')
     or pmd-java:typeIs('javax.ejb.EJBLocalObject')
     or pmd-java:typeIs('javax.ejb.EJBLocalHome')
     or pmd-java:typeIs('javax.ejb.EJBObject')
    ]]
    /ClassOrInterfaceBody/FieldDeclaration
        [pmd-java:modifiers() = 'static']
        [not(pmd-java:modifiers() = 'final')]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class SomeEJB extends EJBObject implements EJBLocalHome {

    private static int CountA;          // poor, field can be edited

    private static final int CountB;    // preferred, read-only access
}
]]>
        </example>
    </rule>

    <rule name="StringBufferInstantiationWithChar"
          language="java"
          since="3.9"
          message="Do not instantiate a StringBuffer or StringBuilder with a char"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#stringbufferinstantiationwithchar">
        <description>
Individual character values provided as initialization arguments will be converted into integers.
This can lead to internal buffer sizes that are larger than expected. Some examples:

```
new StringBuffer()      //  16
new StringBuffer(6)     //  6
new StringBuffer("hello world")  // 11 + 16 = 27
new StringBuffer('A')   //  chr(A) = 65
new StringBuffer("A")   //  1 + 16 = 17

new StringBuilder()     //  16
new StringBuilder(6)    //  6
new StringBuilder("hello world")  // 11 + 16 = 27
new StringBuilder('C')   //  chr(C) = 67
new StringBuilder("A")   //  1 + 16 = 17
```
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ConstructorCall[ArgumentList/CharLiteral]
    [pmd-java:typeIs('java.lang.StringBuilder') or pmd-java:typeIs('java.lang.StringBuffer')]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
// misleading instantiation, these buffers
// are actually sized to 99 characters long
StringBuffer  sb1 = new StringBuffer('c');
StringBuilder sb2 = new StringBuilder('c');

// in these forms, just single characters are allocated
StringBuffer  sb3 = new StringBuffer("c");
StringBuilder sb4 = new StringBuilder("c");
]]>
        </example>
    </rule>

    <rule name="SuspiciousEqualsMethodName"
          language="java"
          since="2.0"
          message="The method name and parameter number are suspiciously close to equals(Object)"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#suspiciousequalsmethodname">
        <description>
The method name and parameter number are suspiciously close to `Object.equals`, which can denote an
intention to override it. However, the method does not override `Object.equals`, but overloads it instead.
Overloading `Object.equals` method is confusing for other programmers, error-prone and hard to maintain,
especially when using inheritance, because `@Override` annotations used in subclasses can provide a false
sense of security. For more information on `Object.equals` method, see Effective Java, 3rd Edition,
Item 10: Obey the general contract when overriding equals.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodDeclaration[@Name = 'equals'][
    (@Arity = 1
     and not(FormalParameters/FormalParameter[pmd-java:typeIsExactly('java.lang.Object')])
     or not(PrimitiveType[@Kind = 'boolean'])
    ) or (
     @Arity = 2
     and PrimitiveType[@Kind = 'boolean']
     and FormalParameters/FormalParameter[pmd-java:typeIsExactly('java.lang.Object')]
     and not(pmd-java:hasAnnotation('java.lang.Override'))
    )
]
| //MethodDeclaration[@Name = 'equal'][
    @Arity = 1
    and FormalParameters/FormalParameter[pmd-java:typeIsExactly('java.lang.Object')]
]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
   public int equals(Object o) {
     // oops, this probably was supposed to be boolean equals
   }
   public boolean equals(String s) {
     // oops, this probably was supposed to be equals(Object)
   }
   public boolean equals(Object o1, Object o2) {
     // oops, this probably was supposed to be equals(Object)
   }
}
]]>
        </example>
    </rule>

    <rule name="SuspiciousHashcodeMethodName"
          language="java"
          since="1.5"
          message="The method name and return type are suspiciously close to hashCode()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#suspicioushashcodemethodname">
        <description>
The method name and return type are suspiciously close to hashCode(), which may denote an intention
to override the hashCode() method.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[
        lower-case(@Name) = 'hashcode'
    and @Name != 'hashCode'
    and @Arity = 0
    and PrimitiveType[@Kind = 'int']
]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    public int hashcode() { // oops, this probably was supposed to be 'hashCode'
    }
}
]]>
        </example>
    </rule>

    <rule name="SuspiciousOctalEscape"
          language="java"
          since="1.5"
          message="Suspicious decimal characters following octal escape in string literal: {0}"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SuspiciousOctalEscapeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#suspiciousoctalescape">
        <description>
A suspicious octal escape sequence was found inside a String literal.
The Java language specification (section 3.10.6) says an octal
escape sequence inside a literal String shall consist of a backslash
followed by:

    OctalDigit | OctalDigit OctalDigit | ZeroToThree OctalDigit OctalDigit

Any octal escape sequence followed by non-octal digits can be confusing,
e.g. "\038" is interpreted as the octal escape sequence "\03" followed by
the literal character "8".
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
public void foo() {
  // interpreted as octal 12, followed by character '8'
  System.out.println("suspicious: \128");
}
]]>
        </example>
    </rule>

    <rule name="TestClassWithoutTestCases"
          language="java"
          since="3.0"
          message="The class ''{0}'' might be a test class, but it contains no test cases."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.TestClassWithoutTestCasesRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#testclasswithouttestcases">
        <description>
Test classes typically end with the suffix "Test", "Tests" or "TestCase". Having a non-test class with that name
is not a good practice, since most people will assume it is a test case. Test classes have test methods
named "testXXX" (JUnit3) or use annotations (e.g. `@Test`).

The suffix can be configured using the property `testClassPattern`. To disable the detection of possible test classes
by name, set this property to an empty string.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
//Consider changing the name of the class if it is not a test
//Consider adding test methods if it is a test
public class CarTest {
   public static void main(String[] args) {
    // do something
   }
   // code
}
]]>
        </example>
    </rule>

    <rule name="UnconditionalIfStatement"
          language="java"
          since="1.5"
          message="Do not use 'if' statements that are always true or always false"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unconditionalifstatement">
        <description>
Do not use "if" statements whose conditionals are always true or always false.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
 <![CDATA[
//IfStatement[BooleanLiteral[1]]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    public void close() {
        if (true) {        // fixed conditional, not recommended
            // ...
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="UnnecessaryBooleanAssertion"
          language="java"
          since="3.0"
          message="assertTrue(true) or similar statements are unnecessary"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unnecessarybooleanassertion">
        <description>
A JUnit test assertion with a boolean literal is unnecessary since it always will evaluate to the same thing.
Consider using flow control (in case of `assertTrue(false)` or similar) or simply removing
statements like `assertTrue(true)` and `assertFalse(false)`. If you just want a test to halt after finding
an error, use the `fail()` method and provide an indication message of why it did.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//ClassOrInterfaceDeclaration
    [pmd-java:typeIs('junit.framework.TestCase')
     or .//Annotation[pmd-java:typeIs('org.junit.Test')
                   or pmd-java:typeIs('org.junit.jupiter.api.Test')
                   or pmd-java:typeIs('org.junit.jupiter.api.RepeatedTest')
                   or pmd-java:typeIs('org.junit.jupiter.api.TestFactory')
                   or pmd-java:typeIs('org.junit.jupiter.api.TestTemplate')
                   or pmd-java:typeIs('org.junit.jupiter.params.ParameterizedTest')
     ]
    ]
    //MethodCall[@MethodName = ('assertTrue', 'assertFalse')]
        [ArgumentList
            [
                BooleanLiteral or
                UnaryExpression[@Operator = '!'][BooleanLiteral]
            ]
        ]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class SimpleTest extends TestCase {
    public void testX() {
        assertTrue(true);            // serves no real purpose - remove it
    }
}
]]>
        </example>
    </rule>

    <rule name="UnnecessaryCaseChange"
          language="java"
          since="3.3"
          message="Using equalsIgnoreCase() is cleaner than using toUpperCase/toLowerCase().equals()."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.UnnecessaryCaseChangeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unnecessarycasechange">
        <description>
Using equalsIgnoreCase() is faster than using toUpperCase/toLowerCase().equals()
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
boolean answer1 = buz.toUpperCase().equals("BAZ");              // should be buz.equalsIgnoreCase("BAZ")

boolean answer2 = buz.toUpperCase().equalsIgnoreCase("BAZ");    // another unnecessary toUpperCase()
]]>
        </example>
    </rule>

    <rule name="UnnecessaryConversionTemporary"
          language="java"
          since="0.1"
          message="Avoid unnecessary temporaries when converting primitives to Strings"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unnecessaryconversiontemporary">
        <description>
Avoid the use temporary objects when converting primitives to Strings. Use the static conversion methods
on the wrapper classes instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall[@MethodName = 'toString']
    [ConstructorCall[position() = 1]
        [
            pmd-java:typeIs('java.lang.Integer')
         or pmd-java:typeIs('java.lang.Long')
         or pmd-java:typeIs('java.lang.Float')
         or pmd-java:typeIs('java.lang.Byte')
         or pmd-java:typeIs('java.lang.Double')
         or pmd-java:typeIs('java.lang.Short')
        ]
    ]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public String convert(int x) {
    String foo = new Integer(x).toString(); // this wastes an object

    return Integer.toString(x);             // preferred approach
}
]]>
        </example>
    </rule>

    <rule name="UnusedNullCheckInEquals"
          language="java"
          since="3.5"
          message="Invoke equals() on the object you''ve already ensured is not null"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unusednullcheckinequals">
        <description>
After checking an object reference for null, you should invoke equals() on that object rather than passing
it to another object's equals() method.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//InfixExpression[@Operator = '&&']
  /MethodCall[pmd-java:matchesSig("java.lang.Object#equals(java.lang.Object)")]
             [not(StringLiteral)]
             [not(VariableAccess[@CompileTimeConstant = true()])]
             [ArgumentList/VariableAccess/@Name = ..//InfixExpression[@Operator = '!='][NullLiteral]/VariableAccess/@Name]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Test {

    public String method1() { return "ok";}
    public String method2() { return null;}

    public void method(String a) {
        String b;
        // I don't know it method1() can be "null"
        // but I know "a" is not null..
        // I'd better write a.equals(method1())

        if (a!=null && method1().equals(a)) { // will trigger the rule
            //whatever
        }

        if (method1().equals(a) && a != null) { // won't trigger the rule
            //whatever
        }

        if (a!=null && method1().equals(b)) { // won't trigger the rule
            //whatever
        }

        if (a!=null && "LITERAL".equals(a)) { // won't trigger the rule
            //whatever
        }

        if (a!=null && !a.equals("go")) { // won't trigger the rule
            a=method2();
            if (method1().equals(a)) {
                //whatever
            }
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="UseCorrectExceptionLogging"
          language="java"
          since="3.2"
          message="Use the correct logging statement for logging exceptions"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#usecorrectexceptionlogging">
        <description>
To make sure the full stacktrace is printed out, use the logging statement with two arguments: a String and a Throwable.

This rule only applies to [Apache Commons Logging](https://commons.apache.org/proper/commons-logging/).
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//CatchClause/Block//MethodCall
    [pmd-java:matchesSig('org.apache.commons.logging.Log#_(java.lang.Object)')]
    [ArgumentList[not(MethodCall)]//VariableAccess/@Name = ancestor::CatchClause/CatchParameter/@Name]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Main {
    private static final Log _LOG = LogFactory.getLog( Main.class );
    void bar() {
        try {
        } catch( Exception e ) {
            _LOG.error( e ); //Wrong!
        } catch( OtherException oe ) {
            _LOG.error( oe.getMessage(), oe ); //Correct
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="UseEqualsToCompareStrings"
          language="java"
          since="4.1"
          message="Use equals() to compare strings instead of ''=='' or ''!=''"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#useequalstocomparestrings">
        <description>
Using '==' or '!=' to compare strings is only reliable if the interned string (`String#intern()`)
is used on both sides.

Use the `equals()` method instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//InfixExpression[@Operator = ('==', '!=')]
                 [count(*[pmd-java:typeIsExactly('java.lang.String')]) = 2]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
public boolean test(String s) {
    if (s == "one") return true;        // unreliable
    if ("two".equals(s)) return true;   // better
    return false;
}
]]>
        </example>
    </rule>

    <rule name="UselessOperationOnImmutable"
          language="java"
          since="3.5"
          message="An operation on an Immutable object (String, BigDecimal or BigInteger) won't change the object itself"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.UselessOperationOnImmutableRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#uselessoperationonimmutable">
        <description>
An operation on an Immutable object (String, BigDecimal or BigInteger) won't change the object itself
since the result of the operation is a new object. Therefore, ignoring the operation result is an error.
        </description>
        <priority>3</priority>
        <example>
<![CDATA[
import java.math.*;

class Test {
    void method1() {
        BigDecimal bd=new BigDecimal(10);
        bd.add(new BigDecimal(5));      // this will trigger the rule
    }
    void method2() {
        BigDecimal bd=new BigDecimal(10);
        bd = bd.add(new BigDecimal(5)); // this won't trigger the rule
    }
}
]]>
        </example>
    </rule>

    <rule name="UseLocaleWithCaseConversions"
          language="java"
          since="2.0"
          message="When doing a String.toLowerCase()/toUpperCase() call, use a Locale"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#uselocalewithcaseconversions">
        <description>
When doing `String::toLowerCase()/toUpperCase()` conversions, use an explicit locale argument to specify the case
transformation rules.

Using `String::toLowerCase()` without arguments implicitly uses `Locale::getDefault()`.
The problem is that the default locale depends on the current JVM setup (and usually on the system in which
it is running). Using the system default may be exactly what you want (e.g. if you are manipulating strings
you got through standard input), but it may as well not be the case (e.g. if you are getting the string over
the network or a file, and the encoding is well-defined and independent of the environment). In the latter case,
using the default locale makes the case transformation brittle, as it may yield unexpected results on a machine
whose locale has other case translation rules. For example, in Turkish, the uppercase form of `i` is `İ` (U+0130,
not ASCII) and not `I` (U+0049) as in English.

The rule is intended to *force* developers to think about locales when dealing with strings. By taking a
conscious decision about the choice of locale at the time of writing, you reduce the risk of surprising
behaviour down the line, and communicate your intent to future readers.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
<![CDATA[
//MethodCall[pmd-java:matchesSig("java.lang.String#toLowerCase()") or pmd-java:matchesSig("java.lang.String#toUpperCase()")]
            [not(MethodCall[@MethodName = "toHexString"])]
]]>
                </value>
            </property>
        </properties>
        <example>
<![CDATA[
// violation - implicitly system-dependent conversion
if (x.toLowerCase().equals("list")) {}

// The above will not match "LIST" on a system with a Turkish locale.
// It could be replaced with
if (x.toLowerCase(Locale.US).equals("list")) { }
// or simply
if (x.equalsIgnoreCase("list")) { }

// ok - system independent conversion
String z = a.toLowerCase(Locale.ROOT);

// ok - explicit system-dependent conversion
String z2 = a.toLowerCase(Locale.getDefault());
]]>
        </example>
    </rule>

    <rule name="UseProperClassLoader"
          language="java"
          since="3.7"
          message="In J2EE, getClassLoader() might not work as expected.  Use Thread.currentThread().getContextClassLoader() instead."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#useproperclassloader">
        <description>
In J2EE, the getClassLoader() method might not work as expected. Use
Thread.currentThread().getContextClassLoader() instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//MethodCall[pmd-java:matchesSig("java.lang.Class#getClassLoader()")]</value>
            </property>
        </properties>
        <example>
<![CDATA[
public class Foo {
    ClassLoader cl = Bar.class.getClassLoader();
}
]]>
        </example>
    </rule>

</ruleset>