001 /*
002 * JBoss DNA (http://www.jboss.org/dna)
003 * See the COPYRIGHT.txt file distributed with this work for information
004 * regarding copyright ownership. Some portions may be licensed
005 * to Red Hat, Inc. under one or more contributor license agreements.
006 * See the AUTHORS.txt file in the distribution for a full listing of
007 * individual contributors.
008 *
009 * JBoss DNA is free software. Unless otherwise indicated, all code in JBoss DNA
010 * is licensed to you under the terms of the GNU Lesser General Public License as
011 * published by the Free Software Foundation; either version 2.1 of
012 * the License, or (at your option) any later version.
013 *
014 * JBoss DNA is distributed in the hope that it will be useful,
015 * but WITHOUT ANY WARRANTY; without even the implied warranty of
016 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
017 * Lesser General Public License for more details.
018 *
019 * You should have received a copy of the GNU Lesser General Public
020 * License along with this software; if not, write to the Free
021 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
022 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
023 */
024 package org.jboss.dna.common.util;
025
026 import java.util.Arrays;
027
028 /**
029 * Utilities for easily computing hash codes. The algorithm should generally produce good distributions for use in hash-based
030 * containers or collections, but as expected does always result in repeatable hash codes given the inputs.
031 * @author Randall Hauch
032 */
033 public class HashCode {
034
035 // Prime number used in improving distribution: 1,000,003
036 private static final int PRIME = 103;
037
038 /**
039 * Compute a combined hash code from the supplied objects. This method always returns 0 if no objects are supplied.
040 * @param objects the objects that should be used to compute the hash code
041 * @return the hash code
042 */
043 public static int compute( Object... objects ) {
044 return compute(0, objects);
045 }
046
047 /**
048 * Compute a combined hash code from the supplied objects using the supplied seed.
049 * @param seed a value upon which the hash code will be based; may be 0
050 * @param objects the objects that should be used to compute the hash code
051 * @return the hash code
052 */
053 protected static int compute( int seed, Object... objects ) {
054 if (objects == null || objects.length == 0) {
055 return seed * HashCode.PRIME;
056 }
057 // Compute the hash code for all of the objects ...
058 int hc = seed;
059 for (Object object : objects) {
060 hc = HashCode.PRIME * hc;
061 if (object instanceof byte[]) {
062 hc += Arrays.hashCode((byte[])object);
063 } else if (object instanceof boolean[]) {
064 hc += Arrays.hashCode((boolean[])object);
065 } else if (object instanceof short[]) {
066 hc += Arrays.hashCode((short[])object);
067 } else if (object instanceof int[]) {
068 hc += Arrays.hashCode((int[])object);
069 } else if (object instanceof long[]) {
070 hc += Arrays.hashCode((long[])object);
071 } else if (object instanceof float[]) {
072 hc += Arrays.hashCode((float[])object);
073 } else if (object instanceof double[]) {
074 hc += Arrays.hashCode((double[])object);
075 } else if (object instanceof char[]) {
076 hc += Arrays.hashCode((char[])object);
077 } else if (object instanceof Object[]) {
078 hc += Arrays.hashCode((Object[])object);
079 } else if (object != null) {
080 hc += object.hashCode();
081 }
082 }
083 return hc;
084 }
085
086 }