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DiamondOperatorCheck.java
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DiamondOperatorCheck.java
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/*
* Copyright (c) 2011-2024 Qulice.com
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met: 1) Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer. 2) Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution. 3) Neither the name of the Qulice.com nor
* the names of its contributors may be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
* NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
* THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.qulice.checkstyle;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
/**
* Checks if possible to use Diamond operator in generic instances creation.
*
* <p>Check is performed for variable declarations. Since parameterized types are invariant
* in generics, Diamond operator should always be used in variable declarations.</p>
*
* <p>For example,
* <pre>
* private List<Number> numbers = new ArrayList<Integer>(); // error
* </pre>
* will return compilation error (because <code>ArrayList<Integer></code> is not
* a subclass of <code>List<Number></code>).
* </p>
* <p>Hence, the only possible way to create a generic instance is copying type arguments from
* the variable declaration.
* <pre>
* private List<Number> numbers = new ArrayList<Number>();
* </pre>
* In that case, Diamond Operator should always be used.
* <pre>
* private List<Number> numbers = new ArrayList<>();
* </pre>
* </p>
* <p>Exceptions to the rule above are wildcards, with them it's possible
* to have different type parameters for left and right parts of variable declaration.
* <pre>
* // will compile
* private List<? extends Number> numbers = new ArrayList<Integer>();
* private List<? super Integer> list = new ArrayList<Number>();
*</pre>
* Although, this is not considered as good codestyle,
* so it's better to use diamond operator here either.
* </p>
*
* @since 0.17
*/
public final class DiamondOperatorCheck extends AbstractCheck {
@Override
public int[] getDefaultTokens() {
return new int[]{TokenTypes.VARIABLE_DEF};
}
@Override
public int[] getAcceptableTokens() {
return this.getDefaultTokens();
}
@Override
public int[] getRequiredTokens() {
return this.getDefaultTokens();
}
@Override
public void visitToken(final DetailAST node) {
final DetailAST generic = DiamondOperatorCheck
.findFirstChildNodeOfType(
node.findFirstToken(TokenTypes.TYPE), TokenTypes.TYPE_ARGUMENTS
);
final DetailAST assign = node.findFirstToken(TokenTypes.ASSIGN);
final DetailAST instance;
if (assign == null || generic == null) {
instance = null;
} else {
instance = assign.getFirstChild().getFirstChild();
}
if (instance != null && instance.getType() == TokenTypes.LITERAL_NEW
&& DiamondOperatorCheck.isNotObjectBlock(instance)
&& DiamondOperatorCheck.isNotArray(instance)) {
final DetailAST type =
DiamondOperatorCheck.findFirstChildNodeOfType(
instance, TokenTypes.TYPE_ARGUMENTS
);
if (!DiamondOperatorCheck.isDiamondOperatorUsed(type)) {
log(type, "Use diamond operator");
}
}
}
/**
* Checks if node is not array.
*
* @param node Node
* @return True if not array
*/
private static boolean isNotArray(final DetailAST node) {
return node.findFirstToken(TokenTypes.ARRAY_DECLARATOR) == null;
}
/**
* Checks if node is object block.
*
* @param node Node
* @return True if not object block
*/
private static boolean isNotObjectBlock(final DetailAST node) {
return node.getLastChild().getType() != TokenTypes.OBJBLOCK;
}
/**
* Checks if node contains empty set of type parameters and
* comprises angle brackets only (<>).
* @param node Node of type arguments
* @return True if node contains angle brackets only
*/
private static boolean isDiamondOperatorUsed(final DetailAST node) {
return node.getChildCount() == 2
&& node.getFirstChild().getType() == TokenTypes.GENERIC_START
&& node.getLastChild().getType() == TokenTypes.GENERIC_END;
}
/**
* Returns the first child node of a specified type.
*
* @param node AST subtree to process.
* @param type Type of token
* @return Child node of specified type
*/
private static DetailAST findFirstChildNodeOfType(
final DetailAST node, final int type
) {
DetailAST result = node.findFirstToken(type);
if (result == null) {
final DetailAST child = node.getFirstChild();
if (child != null) {
result = DiamondOperatorCheck
.findFirstChildNodeOfType(child, type);
}
}
return result;
}
}