HashCode.java

/*
 * ModeShape (http://www.modeshape.org)
 *
 * 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.modeshape.schematic.internal;

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.
 */
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;
    }

}