Computing hash codes
/*
* JBoss DNA (http://www.jboss.org/dna)
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership. Some portions may be licensed
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* See the AUTHORS.txt file in the distribution for a full listing of
* individual contributors.
*
* JBoss DNA is free software. Unless otherwise indicated, all code in JBoss DNA
* is licensed to you under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
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*
* JBoss DNA is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
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*/
import java.util.Arrays;
/**
* Utilities for easily computing hash codes. The algorithm should generally produce good distributions for use in hash-based
* containers or collections, but as expected does always result in repeatable hash codes given the inputs.
* @author Randall Hauch
*/
public class HashCode {
// Prime number used in improving distribution: 1,000,003
private static final int PRIME = 103;
/**
* Compute a combined hash code from the supplied objects. This method always returns 0 if no objects are supplied.
* @param objects the objects that should be used to compute the hash code
* @return the hash code
*/
public static int compute( Object... objects ) {
return compute(0, objects);
}
/**
* Compute a combined hash code from the supplied objects using the supplied seed.
* @param seed a value upon which the hash code will be based; may be 0
* @param objects the objects that should be used to compute the hash code
* @return the hash code
*/
protected static int compute( int seed, Object... objects ) {
if (objects == null || objects.length == 0) {
return seed * HashCode.PRIME;
}
// Compute the hash code for all of the objects ...
int hc = seed;
for (Object object : objects) {
hc = HashCode.PRIME * hc;
if (object instanceof byte[]) {
hc += Arrays.hashCode((byte[])object);
} else if (object instanceof boolean[]) {
hc += Arrays.hashCode((boolean[])object);
} else if (object instanceof short[]) {
hc += Arrays.hashCode((short[])object);
} else if (object instanceof int[]) {
hc += Arrays.hashCode((int[])object);
} else if (object instanceof long[]) {
hc += Arrays.hashCode((long[])object);
} else if (object instanceof float[]) {
hc += Arrays.hashCode((float[])object);
} else if (object instanceof double[]) {
hc += Arrays.hashCode((double[])object);
} else if (object instanceof char[]) {
hc += Arrays.hashCode((char[])object);
} else if (object instanceof Object[]) {
hc += Arrays.hashCode((Object[])object);
} else if (object != null) {
hc += object.hashCode();
}
}
return hc;
}
}
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