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/*
* 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;
/**
* Assists in implementing {@link Object#hashCode()} methods.
*
* This class enables a good hashCode method to be built for any class. It
* follows the rules laid out in the book
* Effective Java
* by Joshua Bloch. Writing a good hashCode method is actually quite
* difficult. This class aims to simplify the process.
*
* All relevant fields from the object should be included in the
* hashCode method. Derived fields may be excluded. In general, any
* field used in the equals method must be used in the hashCode
* method.
*
* To use this class write code as follows:
*
* public class Person {
* String name;
* int age;
* boolean isSmoker;
* ...
*
* 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();
* }
* }
*
*
* If required, the superclass hashCode() can be added
* using {@link #appendSuper}.
*
* Alternatively, there is a method that uses reflection to determine
* the fields to test. Because these fields are usually private, the method,
* reflectionHashCode, uses AccessibleObject.setAccessible 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.
*
* A typical invocation for this method would look like:
*
* public int hashCode() {
* return HashCodeBuilder.reflectionHashCode(this);
* }
*
*
* @author Stephen Colebourne
* @author Gary Gregory
* @author Pete Gieser
* @since 1.0
* @version $Id: HashCodeBuilder.java 161243 2005-04-14 04:30:28Z ggregory $
*/
public class HashCodeBuilder {
/**
* Constant to use in building the hashCode.
*/
private final int iConstant;
/**
* Running total of the hashCode.
*/
private int iTotal = 0;
/**
* Uses two hard coded choices for the constants
* needed to build a hashCode.
*/
public HashCodeBuilder() {
iConstant = 37;
iTotal = 17;
}
/**
* 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.
*
* @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;
}
//-------------------------------------------------------------------------
/**
* This method uses reflection to build a valid hash code.
*
* This constructor uses two hard coded choices for the constants
* needed to build a hash code.
*
* It uses AccessibleObject.setAccessible 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.
*
* Transient members will be not be used, as they are likely derived
* fields, and not part of the value of the Object.
*
* Static fields will not be tested. Superclass fields will be included.
*
* @param object the Object to create a hashCode for
* @return int hash code
* @throws IllegalArgumentException if the object is null
*/
public static int reflectionHashCode(Object object) {
return reflectionHashCode(17, 37, object, false, null);
}
/**
* This method uses reflection to build a valid hash code.
*
* This constructor uses two hard coded choices for the constants needed
* to build a hash code.
*
* It uses AccessibleObject.setAccessible 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.
*
* If the TestTransients parameter is set to true, transient
* members will be tested, otherwise they are ignored, as they are likely
* derived fields, and not part of the value of the Object.
*
* Static fields will not be tested. Superclass fields will be included.
*
* @param object the Object to create a hashCode for
* @param testTransients whether to include transient fields
* @return int hash code
* @throws IllegalArgumentException if the object is null
*/
public static int reflectionHashCode(Object object, boolean testTransients) {
return reflectionHashCode(17, 37, object, testTransients, null);
}
/**
* This method uses reflection to build a valid hash code.
*
* It uses AccessibleObject.setAccessible 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.
*
* Transient members will be not be used, as they are likely derived
* fields, and not part of the value of the Object.
*
* Static fields will not be tested. Superclass fields will be included.
*
* 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.
*
* @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 hashCode for
* @return int hash code
* @throws IllegalArgumentException if the Object is null
* @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);
}
/**
* This method uses reflection to build a valid hash code.
*
* It uses AccessibleObject.setAccessible 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.
*
* If the TestTransients parameter is set to true, transient
* members will be tested, otherwise they are ignored, as they are likely
* derived fields, and not part of the value of the Object.
*
* Static fields will not be tested. Superclass fields will be included.
*
* 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.
*
* @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 hashCode for
* @param testTransients whether to include transient fields
* @return int hash code
* @throws IllegalArgumentException if the Object is null
* @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);
}
/**
* This method uses reflection to build a valid hash code.
*
* It uses AccessibleObject.setAccessible 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.
*
* If the TestTransients parameter is set to true, transient
* members will be tested, otherwise they are ignored, as they are likely
* derived fields, and not part of the value of the Object.
*
* 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.
*
* 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.
*
* @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 hashCode for
* @param testTransients whether to include transient fields
* @param reflectUpToClass the superclass to reflect up to (inclusive),
* may be null
* @return int hash code
* @throws IllegalArgumentException if the Object is null
* @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) {
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);
while (clazz.getSuperclass() != null && clazz != reflectUpToClass) {
clazz = clazz.getSuperclass();
reflectionAppend(object, clazz, builder, testTransients);
}
return builder.toHashCode();
}
/**
* Appends the fields and values defined by the given object of the
* given Class.
*
* @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
*/
private static void reflectionAppend(Object object, Class clazz, HashCodeBuilder builder, boolean useTransients) {
Field[] fields = clazz.getDeclaredFields();
AccessibleObject.setAccessible(fields, true);
for (int i = 0; i < fields.length; i++) {
Field f = fields[i];
if ((f.getName().indexOf('$') == -1)
&& (useTransients || !Modifier.isTransient(f.getModifiers()))
&& (!Modifier.isStatic(f.getModifiers()))) {
try {
builder.append(f.get(object));
} 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");
}
}
}
}
//-------------------------------------------------------------------------
/**
* Adds the result of super.hashCode() to this builder.
*
* @param superHashCode the result of calling super.hashCode()
* @return this HashCodeBuilder, used to chain calls.
* @since 2.0
*/
public HashCodeBuilder appendSuper(int superHashCode) {
iTotal = iTotal * iConstant + superHashCode;
return this;
}
//-------------------------------------------------------------------------
/**
* Append a hashCode for an Object.
*
* @param object the Object to add to the hashCode
* @return this
*/
public HashCodeBuilder append(Object object) {
if (object == null) {
iTotal = iTotal * iConstant;
} else {
if (object.getClass().isArray() == false) {
//the simple case, not an array, just the element
iTotal = iTotal * iConstant + object.hashCode();
} else {
//'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);
}
}
}
return this;
}
/**
* Append a hashCode for a long.
*
* @param value the long to add to the hashCode
* @return this
*/
public HashCodeBuilder append(long value) {
iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
return this;
}
/**
* Append a hashCode for an int.
*
* @param value the int to add to the hashCode
* @return this
*/
public HashCodeBuilder append(int value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for a short.
*
* @param value the short to add to the hashCode
* @return this
*/
public HashCodeBuilder append(short value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for a char.
*
* @param value the char to add to the hashCode
* @return this
*/
public HashCodeBuilder append(char value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for a byte.
*
* @param value the byte to add to the hashCode
* @return this
*/
public HashCodeBuilder append(byte value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for a double.
*
* @param value the double to add to the hashCode
* @return this
*/
public HashCodeBuilder append(double value) {
return append(Double.doubleToLongBits(value));
}
/**
* Append a hashCode for a float.
*
* @param value the float to add to the hashCode
* @return this
*/
public HashCodeBuilder append(float value) {
iTotal = iTotal * iConstant + Float.floatToIntBits(value);
return this;
}
/**
* Append a hashCode for a boolean.
* This adds iConstant * 1 to the hashCode
* and not a 1231 or 1237 as done in java.lang.Boolean.
* This is in accordance with the Effective Java
design.
*
* @param value the boolean to add to the hashCode
* @return this
*/
public HashCodeBuilder append(boolean value) {
iTotal = iTotal * iConstant + (value ? 0 : 1);
return this;
}
/**
* Append a hashCode for an Object array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a long array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for an int array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a short array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a char array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a byte array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a double array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a float array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Append a hashCode for a boolean array.
*
* @param array the array to add to the hashCode
* @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;
}
/**
* Return the computed hashCode.
*
* @return hashCode based on the fields appended
*/
public int toHashCode() {
return iTotal;
}
}