All Downloads are FREE. Search and download functionalities are using the official Maven repository.

com.groupbyinc.common.apache.commons.lang3.builder.HashCodeBuilder Maven / Gradle / Ivy

There is a newer version: 198
Show newest version
/*
 * 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.lang3.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.lang3.ArrayUtils;
import org.apache.commons.lang3.Validate;

/**
 * 

* 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. *

* *

* 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 hash code of 674, namely 17 * 37 + 45. *

* *

* 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 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();
 *   }
 * }
 * 
* *

* 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);
 * }
 * 
* *

The {@link HashCodeExclude} annotation can be used to exclude fields from being * used by the reflectionHashCode methods.

* * @since 1.0 */ public class HashCodeBuilder implements Builder { /** * The default initial value to use in reflection hash code building. */ private static final int DEFAULT_INITIAL_VALUE = 17; /** * The default multiplier value to use in reflection hash code building. */ private static final int DEFAULT_MULTIPLIER_VALUE = 37; /** *

* A registry of objects used by reflection methods to detect cyclical object references and avoid infinite loops. *

* * @since 2.3 */ private static final ThreadLocal> REGISTRY = new ThreadLocal<>(); /* * NOTE: 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 hash code 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.identityHashCode() * 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. */ /** *

* Returns the registry of objects being traversed by the reflection methods in the current thread. *

* * @return Set the registry of objects being traversed * @since 2.3 */ static Set getRegistry() { return REGISTRY.get(); } /** *

* Returns true if the registry contains the given object. Used by the reflection methods to avoid * infinite loops. *

* * @param value * The object to lookup in the registry. * @return boolean true if the registry contains the given object. * @since 2.3 */ static boolean isRegistered(final Object value) { final Set registry = getRegistry(); return registry != null && registry.contains(new IDKey(value)); } /** *

* 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 * @param excludeFields * Collection of String field names to exclude from use in calculation of hash code */ private static void reflectionAppend(final Object object, final Class clazz, final HashCodeBuilder builder, final boolean useTransients, final String[] excludeFields) { if (isRegistered(object)) { return; } try { register(object); final Field[] fields = clazz.getDeclaredFields(); AccessibleObject.setAccessible(fields, true); for (final Field field : fields) { if (!ArrayUtils.contains(excludeFields, field.getName()) && !field.getName().contains("$") && (useTransients || !Modifier.isTransient(field.getModifiers())) && !Modifier.isStatic(field.getModifiers()) && !field.isAnnotationPresent(HashCodeExclude.class)) { try { final Object fieldValue = field.get(object); builder.append(fieldValue); } catch (final 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); } } /** *

* Uses reflection to build a valid hash code from the fields of {@code object}. *

* *

* 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. This will be the returned * value if no fields are found to include in the hash code * @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 * * @see HashCodeExclude */ public static int reflectionHashCode(final int initialNonZeroOddNumber, final int multiplierNonZeroOddNumber, final Object object) { return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, false, null); } /** *

* Uses reflection to build a valid hash code from the fields of {@code object}. *

* *

* 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. This will be the returned * value if no fields are found to include in the hash code * @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 * * @see HashCodeExclude */ public static int reflectionHashCode(final int initialNonZeroOddNumber, final int multiplierNonZeroOddNumber, final Object object, final boolean testTransients) { return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients, null); } /** *

* Uses reflection to build a valid hash code from the fields of {@code object}. *

* *

* 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 * the type of the object involved * @param initialNonZeroOddNumber * a non-zero, odd number used as the initial value. This will be the returned * value if no fields are found to include in the hash code * @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 * @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 null * @throws IllegalArgumentException * if the number is zero or even * * @see HashCodeExclude * @since 2.0 */ public static int reflectionHashCode(final int initialNonZeroOddNumber, final int multiplierNonZeroOddNumber, final T object, final boolean testTransients, final Class reflectUpToClass, final String... excludeFields) { Validate.isTrue(object != null, "The object to build a hash code for must not be null"); final 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(); } /** *

* Uses reflection to build a valid hash code from the fields of {@code object}. *

* *

* 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. If no fields are found to include * in the hash code, the result of this method will be constant. *

* * @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 * * @see HashCodeExclude */ public static int reflectionHashCode(final Object object, final boolean testTransients) { return reflectionHashCode(DEFAULT_INITIAL_VALUE, DEFAULT_MULTIPLIER_VALUE, object, testTransients, null); } /** *

* Uses reflection to build a valid hash code from the fields of {@code object}. *

* *

* 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. If no fields are found to include * in the hash code, the result of this method will be constant. *

* * @param object * the Object to create a hashCode 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 null * * @see HashCodeExclude */ public static int reflectionHashCode(final Object object, final Collection excludeFields) { return reflectionHashCode(object, ReflectionToStringBuilder.toNoNullStringArray(excludeFields)); } // ------------------------------------------------------------------------- /** *

* Uses reflection to build a valid hash code from the fields of {@code object}. *

* *

* 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. If no fields are found to include * in the hash code, the result of this method will be constant. *

* * @param object * the Object to create a hashCode 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 null * * @see HashCodeExclude */ public static int reflectionHashCode(final Object object, final String... excludeFields) { return reflectionHashCode(DEFAULT_INITIAL_VALUE, DEFAULT_MULTIPLIER_VALUE, object, false, null, excludeFields); } /** *

* Registers the given object. Used by the reflection methods to avoid infinite loops. *

* * @param value * The object to register. */ private static void register(final Object value) { Set registry = getRegistry(); if (registry == null) { registry = new HashSet<>(); REGISTRY.set(registry); } registry.add(new IDKey(value)); } /** *

* Unregisters the given object. *

* *

* Used by the reflection methods to avoid infinite loops. * * @param value * The object to unregister. * @since 2.3 */ private static void unregister(final Object value) { final Set registry = getRegistry(); if (registry != null) { registry.remove(new IDKey(value)); if (registry.isEmpty()) { REGISTRY.remove(); } } } /** * 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, 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 initialOddNumber * an odd number used as the initial value * @param multiplierOddNumber * an odd number used as the multiplier * @throws IllegalArgumentException * if the number is even */ public HashCodeBuilder(final int initialOddNumber, final int multiplierOddNumber) { Validate.isTrue(initialOddNumber % 2 != 0, "HashCodeBuilder requires an odd initial value"); Validate.isTrue(multiplierOddNumber % 2 != 0, "HashCodeBuilder requires an odd multiplier"); iConstant = multiplierOddNumber; iTotal = initialOddNumber; } /** *

* Append a hashCode for a boolean. *

*

* This adds 1 when true, and 0 when false to the hashCode. *

*

* This is in contrast to the standard java.lang.Boolean.hashCode handling, which computes * a hashCode value of 1231 for java.lang.Boolean instances * that represent true or 1237 for java.lang.Boolean instances * that represent false. *

*

* This is in accordance with the Effective Java design. *

* * @param value * the boolean to add to the hashCode * @return this */ public HashCodeBuilder append(final boolean value) { iTotal = iTotal * iConstant + (value ? 0 : 1); return this; } /** *

* Append a hashCode for a boolean array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final boolean[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final boolean element : array) { append(element); } } return this; } // ------------------------------------------------------------------------- /** *

* Append a hashCode for a byte. *

* * @param value * the byte to add to the hashCode * @return this */ public HashCodeBuilder append(final byte value) { iTotal = iTotal * iConstant + value; return this; } // ------------------------------------------------------------------------- /** *

* Append a hashCode for a byte array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final byte[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final byte element : array) { append(element); } } return this; } /** *

* Append a hashCode for a char. *

* * @param value * the char to add to the hashCode * @return this */ public HashCodeBuilder append(final char value) { iTotal = iTotal * iConstant + value; return this; } /** *

* Append a hashCode for a char array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final char[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final char element : array) { append(element); } } return this; } /** *

* Append a hashCode for a double. *

* * @param value * the double to add to the hashCode * @return this */ public HashCodeBuilder append(final double value) { return append(Double.doubleToLongBits(value)); } /** *

* Append a hashCode for a double array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final double[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final double element : array) { append(element); } } return this; } /** *

* Append a hashCode for a float. *

* * @param value * the float to add to the hashCode * @return this */ public HashCodeBuilder append(final float value) { iTotal = iTotal * iConstant + Float.floatToIntBits(value); return this; } /** *

* Append a hashCode for a float array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final float[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final float element : array) { append(element); } } return this; } /** *

* Append a hashCode for an int. *

* * @param value * the int to add to the hashCode * @return this */ public HashCodeBuilder append(final int value) { iTotal = iTotal * iConstant + value; return this; } /** *

* Append a hashCode for an int array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final int[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final int element : array) { append(element); } } return this; } /** *

* Append a hashCode for a long. *

* * @param value * the long to add to the hashCode * @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(final long value) { iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32))); return this; } /** *

* Append a hashCode for a long array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final long[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final long element : array) { append(element); } } return this; } /** *

* Append a hashCode for an Object. *

* * @param object * the Object to add to the hashCode * @return this */ public HashCodeBuilder append(final Object object) { if (object == null) { iTotal = iTotal * iConstant; } else { if (object.getClass().isArray()) { // factor out array case in order to keep method small enough // to be inlined appendArray(object); } else { iTotal = iTotal * iConstant + object.hashCode(); } } return this; } /** *

* Append a hashCode for an array. *

* * @param object * the array to add to the hashCode */ private void appendArray(final Object object) { // '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); } } /** *

* Append a hashCode for an Object array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final Object[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final Object element : array) { append(element); } } return this; } /** *

* Append a hashCode for a short. *

* * @param value * the short to add to the hashCode * @return this */ public HashCodeBuilder append(final short value) { iTotal = iTotal * iConstant + value; return this; } /** *

* Append a hashCode for a short array. *

* * @param array * the array to add to the hashCode * @return this */ public HashCodeBuilder append(final short[] array) { if (array == null) { iTotal = iTotal * iConstant; } else { for (final short element : array) { append(element); } } return this; } /** *

* 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(final int superHashCode) { iTotal = iTotal * iConstant + superHashCode; return this; } /** *

* Return the computed hashCode. *

* * @return hashCode based on the fields appended */ public int toHashCode() { return iTotal; } /** * Returns the computed hashCode. * * @return hashCode based on the fields appended * * @since 3.0 */ @Override public Integer build() { return Integer.valueOf(toHashCode()); } /** *

* The computed hashCode from toHashCode() is returned due to the likelihood * of bugs in mis-calling toHashCode() and the unlikeliness of it mattering what the hashCode for * HashCodeBuilder itself is.

* * @return hashCode based on the fields appended * @since 2.5 */ @Override public int hashCode() { return toHashCode(); } }




© 2015 - 2024 Weber Informatics LLC | Privacy Policy