lang/builder/HashCodeBuilder.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

import org.apache.commons.lang.ArrayUtils;

/**
 * <p>
 * Assists in implementing {@link Object#hashCode()} methods.
 * </p>
 *
 * <p>
 * This class enables a good <code>hashCode</code> method to be built for any class. It follows the rules laid out in
 * the book <a href="http://java.sun.com/docs/books/effective/index.html">Effective Java</a> by Joshua Bloch. Writing a
 * good <code>hashCode</code> method is actually quite difficult. This class aims to simplify the process.
 * </p>
 *
 * <p>
 * The following is the approach taken. When appending a data field, the current total is multiplied by the
 * multiplier then a relevant value
 * for that data type is added. For example, if the current hashCode is 17, and the multiplier is 37, then
 * appending the integer 45 will create a hashcode of 674, namely 17 * 37 + 45.
 * </p>
 *
 * <p>
 * All relevant fields from the object should be included in the <code>hashCode</code> method. Derived fields may be
 * excluded. In general, any field used in the <code>equals</code> method must be used in the <code>hashCode</code>
 * method.
 * </p>
 *
 * <p>
 * To use this class write code as follows:
 * </p>
 *
 * <pre>
 * public class Person {
 *   String name;
 *   int age;
 *   boolean smoker;
 *   ...
 *
 *   public int hashCode() {
 *     // you pick a hard-coded, randomly chosen, non-zero, odd number
 *     // ideally different for each class
 *     return new HashCodeBuilder(17, 37).
 *       append(name).
 *       append(age).
 *       append(smoker).
 *       toHashCode();
 *   }
 * }
 * </pre>
 *
 * <p>
 * If required, the superclass <code>hashCode()</code> can be added using {@link #appendSuper}.
 * </p>
 *
 * <p>
 * Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are
 * usually private, the method, <code>reflectionHashCode</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 int hashCode() {
 *   return HashCodeBuilder.reflectionHashCode(this);
 * }
 * </pre>
 *
 * @author Apache Software Foundation
 * @author Gary Gregory
 * @author Pete Gieser
 * @since 1.0
 * @version $Id: HashCodeBuilder.java 1057009 2011-01-09 19:48:06Z niallp $
 */
public class HashCodeBuilder {
    /**
     * <p>
     * A registry of objects used by reflection methods to detect cyclical object references and avoid infinite loops.
     * </p>
     *
     * @since 2.3
     */
    private static final ThreadLocal REGISTRY = new ThreadLocal();

    /*
     * N.B. we cannot store the actual objects in a HashSet, as that would use the very hashCode()
     * we are in the process of calculating.
     *
     * So we generate a one-to-one mapping from the original object to a new object.
     *
     * Now HashSet uses equals() to determine if two elements with the same hashcode really
     * are equal, so we also need to ensure that the replacement objects are only equal
     * if the original objects are identical.
     *
     * The original implementation (2.4 and before) used the System.indentityHashCode()
     * method - however this is not guaranteed to generate unique ids (e.g. LANG-459)
     *
     * We now use the IDKey helper class (adapted from org.apache.axis.utils.IDKey)
     * to disambiguate the duplicate ids.
     */

    /**
     * <p>
     * Returns the registry of objects being traversed by the reflection methods in the current thread.
     * </p>
     *
     * @return Set the registry of objects being traversed
     * @since 2.3
     */
    static Set getRegistry() {
        return (Set) REGISTRY.get();
    }

    /**
     * <p>
     * Returns <code>true</code> if the registry contains the given object. Used by the reflection methods to avoid
     * infinite loops.
     * </p>
     *
     * @param value
     *            The object to lookup in the registry.
     * @return boolean <code>true</code> if the registry contains the given object.
     * @since 2.3
     */
    static boolean isRegistered(Object value) {
        Set registry = getRegistry();
        return registry != null && registry.contains(new IDKey(value));
    }

    /**
     * <p>
     * Appends the fields and values defined by the given object of the given <code>Class</code>.
     * </p>
     *
     * @param object
     *            the object to append details of
     * @param clazz
     *            the class to append details of
     * @param builder
     *            the builder to append to
     * @param useTransients
     *            whether to use transient fields
     * @param excludeFields
     *            Collection of String field names to exclude from use in calculation of hash code
     */
    private static void reflectionAppend(Object object, Class clazz, HashCodeBuilder builder, boolean useTransients,
            String[] excludeFields) {
        if (isRegistered(object)) {
            return;
        }
        try {
            register(object);
            Field[] fields = clazz.getDeclaredFields();
            AccessibleObject.setAccessible(fields, true);
            for (int i = 0; i < fields.length; i++) {
                Field field = fields[i];
                if (!ArrayUtils.contains(excludeFields, field.getName())
                    && (field.getName().indexOf('$') == -1)
                    && (useTransients || !Modifier.isTransient(field.getModifiers()))
                    && (!Modifier.isStatic(field.getModifiers()))) {
                    try {
                        Object fieldValue = field.get(object);
                        builder.append(fieldValue);
                    } 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");
                    }
                }
            }
        } finally {
            unregister(object);
        }
    }

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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 used, 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>
     *
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital. Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @throws IllegalArgumentException
     *             if the number is zero or even
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, false, null, null);
    }

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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>
     *
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital. Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @throws IllegalArgumentException
     *             if the number is zero or even
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object,
            boolean testTransients) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients, null,
                null);
    }

    /**
     * Calls {@link #reflectionHashCode(int, int, Object, boolean, Class, String[])} with excludeFields set to
     * <code>null</code>.
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @return int hash code
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object,
            boolean testTransients, Class reflectUpToClass) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients,
                reflectUpToClass, null);
    }

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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 included up to and including the specified
     * superclass. A null superclass is treated as java.lang.Object.
     * </p>
     *
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital. Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @param excludeFields
     *            array of field names to exclude from use in calculation of hash code
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @throws IllegalArgumentException
     *             if the number is zero or even
     * @since 2.0
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object,
            boolean testTransients, Class reflectUpToClass, String[] excludeFields) {

        if (object == null) {
            throw new IllegalArgumentException("The object to build a hash code for must not be null");
        }
        HashCodeBuilder builder = new HashCodeBuilder(initialNonZeroOddNumber, multiplierNonZeroOddNumber);
        Class clazz = object.getClass();
        reflectionAppend(object, clazz, builder, testTransients, excludeFields);
        while (clazz.getSuperclass() != null && clazz != reflectUpToClass) {
            clazz = clazz.getSuperclass();
            reflectionAppend(object, clazz, builder, testTransients, excludeFields);
        }
        return builder.toHashCode();
    }

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </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 used, 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 object
     *            the Object to create a <code>hashCode</code> for
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object) {
        return reflectionHashCode(17, 37, object, false, null, null);
    }

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </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 object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object, boolean testTransients) {
        return reflectionHashCode(17, 37, object, testTransients, null, null);
    }

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </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 used, 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 object
     *            the Object to create a <code>hashCode</code> for
     * @param excludeFields
     *            Collection of String field names to exclude from use in calculation of hash code
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object, Collection /* String */excludeFields) {
        return reflectionHashCode(object, ReflectionToStringBuilder.toNoNullStringArray(excludeFields));
    }

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

    /**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </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 used, 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 object
     *            the Object to create a <code>hashCode</code> for
     * @param excludeFields
     *            array of field names to exclude from use in calculation of hash code
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object, String[] excludeFields) {
        return reflectionHashCode(17, 37, object, false, null, excludeFields);
    }

    /**
     * <p>
     * Registers the given object. Used by the reflection methods to avoid infinite loops.
     * </p>
     *
     * @param value
     *            The object to register.
     */
    static void register(Object value) {
        synchronized (HashCodeBuilder.class) {
            if (getRegistry() == null) {
                REGISTRY.set(new HashSet());
            }
        }
        getRegistry().add(new IDKey(value));
    }

    /**
     * <p>
     * Unregisters the given object.
     * </p>
     *
     * <p>
     * Used by the reflection methods to avoid infinite loops.
     *
     * @param value
     *            The object to unregister.
     * @since 2.3
     */
    static void unregister(Object value) {
        Set registry = getRegistry();
        if (registry != null) {
            registry.remove(new IDKey(value));
            synchronized (HashCodeBuilder.class) {
                //read again
                registry = getRegistry();
                if (registry != null && registry.isEmpty()) {
                    REGISTRY.set(null);
                }
            }
        }
    }

    /**
     * Constant to use in building the hashCode.
     */
    private final int iConstant;

    /**
     * Running total of the hashCode.
     */
    private int iTotal = 0;

    /**
     * <p>
     * Uses two hard coded choices for the constants needed to build a <code>hashCode</code>.
     * </p>
     */
    public HashCodeBuilder() {
        iConstant = 37;
        iTotal = 17;
    }

    /**
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital.
     * </p>
     *
     * <p>
     * Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @throws IllegalArgumentException
     *             if the number is zero or even
     */
    public HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber) {
        if (initialNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero initial value");
        }
        if (initialNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd initial value");
        }
        if (multiplierNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero multiplier");
        }
        if (multiplierNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd multiplier");
        }
        iConstant = multiplierNonZeroOddNumber;
        iTotal = initialNonZeroOddNumber;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>boolean</code>.
     * </p>
     * <p>
     * This adds <code>1</code> when true, and <code>0</code> when false to the <code>hashCode</code>.
     * </p>
     * <p>
     * This is in contrast to the standard <code>java.lang.Boolean.hashCode</code> handling, which computes
     * a <code>hashCode</code> value of <code>1231</code> for <code>java.lang.Boolean</code> instances
     * that represent <code>true</code> or <code>1237</code> for <code>java.lang.Boolean</code> instances
     * that represent <code>false</code>.
     * </p>
     * <p>
     * This is in accordance with the <quote>Effective Java</quote> design.
     * </p>
     *
     * @param value
     *            the boolean to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(boolean value) {
        iTotal = iTotal * iConstant + (value ? 0 : 1);
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>boolean</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(boolean[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

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

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>byte</code>.
     * </p>
     *
     * @param value
     *            the byte to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(byte value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

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

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>byte</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(byte[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>char</code>.
     * </p>
     *
     * @param value
     *            the char to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(char value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>char</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(char[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>double</code>.
     * </p>
     *
     * @param value
     *            the double to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(double value) {
        return append(Double.doubleToLongBits(value));
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>double</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(double[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>float</code>.
     * </p>
     *
     * @param value
     *            the float to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(float value) {
        iTotal = iTotal * iConstant + Float.floatToIntBits(value);
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>float</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(float[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for an <code>int</code>.
     * </p>
     *
     * @param value
     *            the int to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(int value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for an <code>int</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(int[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>long</code>.
     * </p>
     *
     * @param value
     *            the long to add to the <code>hashCode</code>
     * @return this
     */
    // NOTE: This method uses >> and not >>> as Effective Java and
    //       Long.hashCode do. Ideally we should switch to >>> at
    //       some stage. There are backwards compat issues, so
    //       that will have to wait for the time being. cf LANG-342.
    public HashCodeBuilder append(long value) {
        iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>long</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(long[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for an <code>Object</code>.
     * </p>
     *
     * @param object
     *            the Object to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(Object object) {
        if (object == null) {
            iTotal = iTotal * iConstant;

        } else {
            if(object.getClass().isArray()) {
                // 'Switch' on type of array, to dispatch to the correct handler
                // This handles multi dimensional arrays
                if (object instanceof long[]) {
                    append((long[]) object);
                } else if (object instanceof int[]) {
                    append((int[]) object);
                } else if (object instanceof short[]) {
                    append((short[]) object);
                } else if (object instanceof char[]) {
                    append((char[]) object);
                } else if (object instanceof byte[]) {
                    append((byte[]) object);
                } else if (object instanceof double[]) {
                    append((double[]) object);
                } else if (object instanceof float[]) {
                    append((float[]) object);
                } else if (object instanceof boolean[]) {
                    append((boolean[]) object);
                } else {
                    // Not an array of primitives
                    append((Object[]) object);
                }
            } else {
                iTotal = iTotal * iConstant + object.hashCode();
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for an <code>Object</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(Object[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>short</code>.
     * </p>
     *
     * @param value
     *            the short to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(short value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>
     * Append a <code>hashCode</code> for a <code>short</code> array.
     * </p>
     *
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(short[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>
     * Adds the result of super.hashCode() to this builder.
     * </p>
     *
     * @param superHashCode
     *            the result of calling <code>super.hashCode()</code>
     * @return this HashCodeBuilder, used to chain calls.
     * @since 2.0
     */
    public HashCodeBuilder appendSuper(int superHashCode) {
        iTotal = iTotal * iConstant + superHashCode;
        return this;
    }

    /**
     * <p>
     * Return the computed <code>hashCode</code>.
     * </p>
     *
     * @return <code>hashCode</code> based on the fields appended
     */
    public int toHashCode() {
        return iTotal;
    }

    /**
     * <p>
     * The computed <code>hashCode</code> from toHashCode() is returned due to the likelyhood
     * of bugs in mis-calling toHashCode() and the unlikelyness of it mattering what the hashCode for
     * HashCodeBuilder itself is.
     *
     * @return <code>hashCode</code> based on the fields appended
     * @since 2.5
     */
    public int hashCode() {
        return toHashCode();
    }

}