EqualsBuilder.java

/*
 * Copyright 2002-2005 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang.builder;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

/**
 * <p>Assists in implementing {@link Object#equals(Object)} methods.</p>
 *
 * <p> This class provides methods to build a good equals method for any
 * class. It follows rules laid out in
 * <a href="http://java.sun.com/docs/books/effective/index.html">Effective Java</a>
 * , by Joshua Bloch. In particular the rule for comparing <code>doubles</code>,
 * <code>floats</code>, and arrays can be tricky. Also, making sure that
 * <code>equals()</code> and <code>hashCode()</code> are consistent can be
 * difficult.</p>
 *
 * <p>Two Objects that compare as equals must generate the same hash code,
 * but two Objects with the same hash code do not have to be equal.</p>
 *
 * <p>All relevant fields should be included in the calculation of equals.
 * Derived fields may be ignored. In particular, any field used in
 * generating a hash code must be used in the equals method, and vice
 * versa.</p>
 *
 * <p>Typical use for the code is as follows:</p>
 * <pre>
 * public boolean equals(Object obj) {
 *   if (obj instanceof MyClass == false) {
 *     return false;
 *   }
 *   if (this == obj) {
 *     return true;
 *   }
 *   MyClass rhs = (MyClass) obj;
 *   return new EqualsBuilder()
 *                 .appendSuper(super.equals(obj))
 *                 .append(field1, rhs.field1)
 *                 .append(field2, rhs.field2)
 *                 .append(field3, rhs.field3)
 *                 .isEquals();
 *  }
 * </pre>
 *
 * <p> Alternatively, there is a method that uses reflection to determine
 * the fields to test. Because these fields are usually private, the method,
 * <code>reflectionEquals</code>, uses <code>AccessibleObject.setAccessible</code> to
 * change the visibility of the fields. This will fail under a security
 * manager, unless the appropriate permissions are set up correctly. It is
 * also slower than testing explicitly.</p>
 *
 * <p> A typical invocation for this method would look like:</p>
 * <pre>
 * public boolean equals(Object obj) {
 *   return EqualsBuilder.reflectionEquals(this, obj);
 * }
 * </pre>
 *
 * @author <a href="mailto:steve.downey@netfolio.com">Steve Downey</a>
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Pete Gieser
 * @author Arun Mammen Thomas
 * @since 1.0
 * @version $Id$
 */
public class EqualsBuilder {
    
    /**
     * If the fields tested are equals.
     * The default value is <code>true</code>.
     */
    private boolean isEquals = true;

    /**
     * <p>Constructor for EqualsBuilder.</p>
     *
     * <p>Starts off assuming that equals is <code>true</code>.</p>
     * @see Object#equals(Object)
     */
    public EqualsBuilder() {
        // do nothing for now.
    }

    //-------------------------------------------------------------------------

    /**
     * <p>This method uses reflection to determine if the two <code>Object</code>s
     * are equal.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is also
     * not as efficient as testing explicitly.</p>
     *
     * <p>Transient members will be not be tested, as they are likely derived
     * fields, and not part of the value of the Object.</p>
     *
     * <p>Static fields will not be tested. Superclass fields will be included.</p>
     *
     * @param lhs  <code>this</code> object
     * @param rhs  the other object
     * @return <code>true</code> if the two Objects have tested equals.
     */
    public static boolean reflectionEquals(Object lhs, Object rhs) {
        return reflectionEquals(lhs, rhs, false, null);
    }

    /**
     * <p>This method uses reflection to determine if the two <code>Object</code>s
     * are equal.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is also
     * not as efficient as testing explicitly.</p>
     *
     * <p>If the TestTransients parameter is set to <code>true</code>, transient
     * members will be tested, otherwise they are ignored, as they are likely
     * derived fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be tested. Superclass fields will be included.</p>
     *
     * @param lhs  <code>this</code> object
     * @param rhs  the other object
     * @param testTransients  whether to include transient fields
     * @return <code>true</code> if the two Objects have tested equals.
     */
    public static boolean reflectionEquals(Object lhs, Object rhs, boolean testTransients) {
        return reflectionEquals(lhs, rhs, testTransients, null);
    }

    /**
     * <p>This method uses reflection to determine if the two <code>Object</code>s
     * are equal.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is also
     * not as efficient as testing explicitly.</p>
     *
     * <p>If the testTransients parameter is set to <code>true</code>, transient
     * members will be tested, otherwise they are ignored, as they are likely
     * derived fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be included. Superclass fields will be appended
     * up to and including the specified superclass. A null superclass is treated
     * as java.lang.Object.</p>
     *
     * @param lhs  <code>this</code> object
     * @param rhs  the other object
     * @param testTransients  whether to include transient fields
     * @param reflectUpToClass  the superclass to reflect up to (inclusive),
     *  may be <code>null</code>
     * @return <code>true</code> if the two Objects have tested equals.
     * @since 2.0
     */
    public static boolean reflectionEquals(Object lhs, Object rhs, boolean testTransients, Class reflectUpToClass) {
        if (lhs == rhs) {
            return true;
        }
        if (lhs == null || rhs == null) {
            return false;
        }
        // Find the leaf class since there may be transients in the leaf 
        // class or in classes between the leaf and root.
        // If we are not testing transients or a subclass has no ivars, 
        // then a subclass can test equals to a superclass.
        Class lhsClass = lhs.getClass();
        Class rhsClass = rhs.getClass();
        Class testClass;
        if (lhsClass.isInstance(rhs)) {
            testClass = lhsClass;
            if (!rhsClass.isInstance(lhs)) {
                // rhsClass is a subclass of lhsClass
                testClass = rhsClass;
            }
        } else if (rhsClass.isInstance(lhs)) {
            testClass = rhsClass;
            if (!lhsClass.isInstance(rhs)) {
                // lhsClass is a subclass of rhsClass
                testClass = lhsClass;
            }
        } else {
            // The two classes are not related.
            return false;
        }
        EqualsBuilder equalsBuilder = new EqualsBuilder();
        try {
            reflectionAppend(lhs, rhs, testClass, equalsBuilder, testTransients);
            while (testClass.getSuperclass() != null && testClass != reflectUpToClass) {
                testClass = testClass.getSuperclass();
                reflectionAppend(lhs, rhs, testClass, equalsBuilder, testTransients);
            }
        } catch (IllegalArgumentException e) {
            // In this case, we tried to test a subclass vs. a superclass and
            // the subclass has ivars or the ivars are transient and 
            // we are testing transients.
            // If a subclass has ivars that we are trying to test them, we get an
            // exception and we know that the objects are not equal.
            return false;
        }
        return equalsBuilder.isEquals();
    }

    /**
     * <p>Appends the fields and values defined by the given object of the
     * given Class.</p>
     * 
     * @param lhs  the left hand object
     * @param rhs  the right hand object
     * @param clazz  the class to append details of
     * @param builder  the builder to append to
     * @param useTransients  whether to test transient fields
     */
    private static void reflectionAppend(
        Object lhs,
        Object rhs,
        Class clazz,
        EqualsBuilder builder,
        boolean useTransients) {
        Field[] fields = clazz.getDeclaredFields();
        AccessibleObject.setAccessible(fields, true);
        for (int i = 0; i < fields.length && builder.isEquals; i++) {
            Field f = fields[i];
            if ((f.getName().indexOf('$') == -1)
                && (useTransients || !Modifier.isTransient(f.getModifiers()))
                && (!Modifier.isStatic(f.getModifiers()))) {
                try {
                    builder.append(f.get(lhs), f.get(rhs));
                } catch (IllegalAccessException e) {
                    //this can't happen. Would get a Security exception instead
                    //throw a runtime exception in case the impossible happens.
                    throw new InternalError("Unexpected IllegalAccessException");
                }
            }
        }
    }

    //-------------------------------------------------------------------------

    /**
     * <p>Adds the result of <code>super.equals()</code> to this builder.</p>
     *
     * @param superEquals  the result of calling <code>super.equals()</code>
     * @return EqualsBuilder - used to chain calls.
     * @since 2.0
     */
    public EqualsBuilder appendSuper(boolean superEquals) {
        if (isEquals == false) {
            return this;
        }
        isEquals = superEquals;
        return this;
    }

    //-------------------------------------------------------------------------

    /**
     * <p>Test if two <code>Object</code>s are equal using their
     * <code>equals</code> method.</p>
     *
     * @param lhs  the left hand object
     * @param rhs  the right hand object
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(Object lhs, Object rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        Class lhsClass = lhs.getClass();
        if (!lhsClass.isArray()) {
            // The simple case, not an array, just test the element
            isEquals = lhs.equals(rhs);
        } else if (lhs.getClass() != rhs.getClass()) {
            // Here when we compare different dimensions, for example: a boolean[][] to a boolean[] 
            this.setEquals(false);
        }
        // 'Switch' on type of array, to dispatch to the correct handler
        // This handles multi dimensional arrays of the same depth
        else if (lhs instanceof long[]) {
            append((long[]) lhs, (long[]) rhs);
        } else if (lhs instanceof int[]) {
            append((int[]) lhs, (int[]) rhs);
        } else if (lhs instanceof short[]) {
            append((short[]) lhs, (short[]) rhs);
        } else if (lhs instanceof char[]) {
            append((char[]) lhs, (char[]) rhs);
        } else if (lhs instanceof byte[]) {
            append((byte[]) lhs, (byte[]) rhs);
        } else if (lhs instanceof double[]) {
            append((double[]) lhs, (double[]) rhs);
        } else if (lhs instanceof float[]) {
            append((float[]) lhs, (float[]) rhs);
        } else if (lhs instanceof boolean[]) {
            append((boolean[]) lhs, (boolean[]) rhs);
        } else {
            // Not an array of primitives
            append((Object[]) lhs, (Object[]) rhs);
        }
        return this;
    }

    /**
     * <p>
     * Test if two <code>long</code> s are equal.
     * </p>
     * 
     * @param lhs
     *                  the left hand <code>long</code>
     * @param rhs
     *                  the right hand <code>long</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(long lhs, long rhs) {
        if (isEquals == false) {
            return this;
        }
        isEquals = (lhs == rhs);
        return this;
    }

    /**
     * <p>Test if two <code>int</code>s are equal.</p>
     *
     * @param lhs  the left hand <code>int</code>
     * @param rhs  the right hand <code>int</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(int lhs, int rhs) {
        if (isEquals == false) {
            return this;
        }
        isEquals = (lhs == rhs);
        return this;
    }

    /**
     * <p>Test if two <code>short</code>s are equal.</p>
     *
     * @param lhs  the left hand <code>short</code>
     * @param rhs  the right hand <code>short</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(short lhs, short rhs) {
        if (isEquals == false) {
            return this;
        }
        isEquals = (lhs == rhs);
        return this;
    }

    /**
     * <p>Test if two <code>char</code>s are equal.</p>
     *
     * @param lhs  the left hand <code>char</code>
     * @param rhs  the right hand <code>char</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(char lhs, char rhs) {
        if (isEquals == false) {
            return this;
        }
        isEquals = (lhs == rhs);
        return this;
    }

    /**
     * <p>Test if two <code>byte</code>s are equal.</p>
     *
     * @param lhs  the left hand <code>byte</code>
     * @param rhs  the right hand <code>byte</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(byte lhs, byte rhs) {
        if (isEquals == false) {
            return this;
        }
        isEquals = (lhs == rhs);
        return this;
    }

    /**
     * <p>Test if two <code>double</code>s are equal by testing that the
     * pattern of bits returned by <code>doubleToLong</code> are equal.</p>
     *
     * <p>This handles NaNs, Infinities, and <code>-0.0</code>.</p>
     *
     * <p>It is compatible with the hash code generated by
     * <code>HashCodeBuilder</code>.</p>
     *
     * @param lhs  the left hand <code>double</code>
     * @param rhs  the right hand <code>double</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(double lhs, double rhs) {
        if (isEquals == false) {
            return this;
        }
        return append(Double.doubleToLongBits(lhs), Double.doubleToLongBits(rhs));
    }

    /**
     * <p>Test if two <code>float</code>s are equal byt testing that the
     * pattern of bits returned by doubleToLong are equal.</p>
     *
     * <p>This handles NaNs, Infinities, and <code>-0.0</code>.</p>
     *
     * <p>It is compatible with the hash code generated by
     * <code>HashCodeBuilder</code>.</p>
     *
     * @param lhs  the left hand <code>float</code>
     * @param rhs  the right hand <code>float</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(float lhs, float rhs) {
        if (isEquals == false) {
            return this;
        }
        return append(Float.floatToIntBits(lhs), Float.floatToIntBits(rhs));
    }

    /**
     * <p>Test if two <code>booleans</code>s are equal.</p>
     *
     * @param lhs  the left hand <code>boolean</code>
     * @param rhs  the right hand <code>boolean</code>
     * @return EqualsBuilder - used to chain calls.
      */
    public EqualsBuilder append(boolean lhs, boolean rhs) {
        if (isEquals == false) {
            return this;
        }
        isEquals = (lhs == rhs);
        return this;
    }

    /**
     * <p>Performs a deep comparison of two <code>Object</code> arrays.</p>
     *
     * <p>This also will be called for the top level of
     * multi-dimensional, ragged, and multi-typed arrays.</p>
     *
     * @param lhs  the left hand <code>Object[]</code>
     * @param rhs  the right hand <code>Object[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(Object[] lhs, Object[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>long</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(long, long)} is used.</p>
     *
     * @param lhs  the left hand <code>long[]</code>
     * @param rhs  the right hand <code>long[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(long[] lhs, long[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>int</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(int, int)} is used.</p>
     *
     * @param lhs  the left hand <code>int[]</code>
     * @param rhs  the right hand <code>int[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(int[] lhs, int[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>short</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(short, short)} is used.</p>
     *
     * @param lhs  the left hand <code>short[]</code>
     * @param rhs  the right hand <code>short[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(short[] lhs, short[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>char</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(char, char)} is used.</p>
     *
     * @param lhs  the left hand <code>char[]</code>
     * @param rhs  the right hand <code>char[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(char[] lhs, char[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>byte</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(byte, byte)} is used.</p>
     *
     * @param lhs  the left hand <code>byte[]</code>
     * @param rhs  the right hand <code>byte[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(byte[] lhs, byte[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>double</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(double, double)} is used.</p>
     *
     * @param lhs  the left hand <code>double[]</code>
     * @param rhs  the right hand <code>double[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(double[] lhs, double[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>float</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(float, float)} is used.</p>
     *
     * @param lhs  the left hand <code>float[]</code>
     * @param rhs  the right hand <code>float[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(float[] lhs, float[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Deep comparison of array of <code>boolean</code>. Length and all
     * values are compared.</p>
     *
     * <p>The method {@link #append(boolean, boolean)} is used.</p>
     *
     * @param lhs  the left hand <code>boolean[]</code>
     * @param rhs  the right hand <code>boolean[]</code>
     * @return EqualsBuilder - used to chain calls.
     */
    public EqualsBuilder append(boolean[] lhs, boolean[] rhs) {
        if (isEquals == false) {
            return this;
        }
        if (lhs == rhs) {
            return this;
        }
        if (lhs == null || rhs == null) {
            this.setEquals(false);
            return this;
        }
        if (lhs.length != rhs.length) {
            this.setEquals(false);
            return this;
        }
        for (int i = 0; i < lhs.length && isEquals; ++i) {
            append(lhs[i], rhs[i]);
        }
        return this;
    }

    /**
     * <p>Returns <code>true</code> if the fields that have been checked
     * are all equal.</p>
     *
     * @return boolean
     */
    public boolean isEquals() {
        return this.isEquals;
    }

    /**
     * Sets the <code>isEquals</code> value.
     * 
     * @param isEquals The value to set.
     * @since 2.1
     */
    protected void setEquals(boolean isEquals) {
        this.isEquals = isEquals;
    }
}