001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.util.hash.composition;
031
032import java.util.ArrayList;
033import java.util.List;
034
035import org.openimaj.util.hash.HashFunction;
036import org.openimaj.util.hash.HashFunctionFactory;
037
038/**
039 * {@link HashComposition}s are {@link HashFunction}s that compose the hash
040 * codes generated by multiple hash functions applied to an object into a single
041 * hash code for that object.
042 *
043 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
044 *
045 * @param <OBJECT>
046 *            Type of object being hashed
047 */
048public abstract class HashComposition<OBJECT> implements HashFunction<OBJECT> {
049        protected List<HashFunction<OBJECT>> hashFunctions;
050
051        /**
052         * Construct with the given functions.
053         *
054         * @param functions
055         *            the underlying hash functions.
056         */
057        public HashComposition(List<HashFunction<OBJECT>> functions) {
058                this.hashFunctions = functions;
059        }
060
061        /**
062         * Construct with the given functions.
063         *
064         * @param first
065         *            the first function
066         * @param remainder
067         *            the remainder of the functions
068         */
069        @SafeVarargs
070        public HashComposition(HashFunction<OBJECT> first, HashFunction<OBJECT>... remainder) {
071                this.hashFunctions = new ArrayList<HashFunction<OBJECT>>();
072                this.hashFunctions.add(first);
073
074                for (final HashFunction<OBJECT> r : remainder)
075                        this.hashFunctions.add(r);
076        }
077
078        /**
079         * Construct with the factory which is used to produce the required number
080         * of functions.
081         *
082         * @param factory
083         *            the factory to use to produce the underlying hash functions.
084         * @param nFuncs
085         *            the number of functions to create for the composition
086         */
087        public HashComposition(HashFunctionFactory<OBJECT> factory, int nFuncs) {
088                this.hashFunctions = new ArrayList<HashFunction<OBJECT>>();
089
090                for (int i = 0; i < nFuncs; i++)
091                        hashFunctions.add(factory.create());
092        }
093}