001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.comparators;
018
019import java.io.Serializable;
020import java.util.Comparator;
021
022import org.apache.commons.collections4.ComparatorUtils;
023import org.apache.commons.collections4.Transformer;
024
025/**
026 * Decorates another Comparator with transformation behavior. That is, the
027 * return value from the transform operation will be passed to the decorated
028 * {@link Comparator#compare(Object,Object) compare} method.
029 * <p>
030 * This class is Serializable from Commons Collections 4.0.
031 * </p>
032 *
033 * @param <I> the input type to the transformer
034 * @param <O> the output type from the transformer
035 *
036 * @since 2.1
037 *
038 * @see org.apache.commons.collections4.Transformer
039 * @see org.apache.commons.collections4.comparators.ComparableComparator
040 */
041public class TransformingComparator<I, O> implements Comparator<I>, Serializable {
042
043    /** Serialization version from Collections 4.0. */
044    private static final long serialVersionUID = 3456940356043606220L;
045
046    /** The decorated comparator. */
047    private final Comparator<O> decorated;
048    /** The transformer being used. */
049    private final Transformer<? super I, ? extends O> transformer;
050
051    //-----------------------------------------------------------------------
052    /**
053     * Constructs an instance with the given Transformer and a
054     * {@link ComparableComparator ComparableComparator}.
055     *
056     * @param transformer what will transform the arguments to <code>compare</code>
057     */
058    public TransformingComparator(final Transformer<? super I, ? extends O> transformer) {
059        this(transformer, ComparatorUtils.NATURAL_COMPARATOR);
060    }
061
062    /**
063     * Constructs an instance with the given Transformer and Comparator.
064     *
065     * @param transformer  what will transform the arguments to <code>compare</code>
066     * @param decorated  the decorated Comparator
067     */
068    public TransformingComparator(final Transformer<? super I, ? extends O> transformer,
069                                  final Comparator<O> decorated) {
070        this.decorated = decorated;
071        this.transformer = transformer;
072    }
073
074    //-----------------------------------------------------------------------
075    /**
076     * Returns the result of comparing the values from the transform operation.
077     *
078     * @param obj1  the first object to transform then compare
079     * @param obj2  the second object to transform then compare
080     * @return negative if obj1 is less, positive if greater, zero if equal
081     */
082    @Override
083    public int compare(final I obj1, final I obj2) {
084        final O value1 = this.transformer.transform(obj1);
085        final O value2 = this.transformer.transform(obj2);
086        return this.decorated.compare(value1, value2);
087    }
088
089    //-----------------------------------------------------------------------
090    /**
091     * Implement a hash code for this comparator that is consistent with
092     * {@link #equals(Object) equals}.
093     *
094     * @return a hash code for this comparator.
095     */
096    @Override
097    public int hashCode() {
098        int total = 17;
099        total = total*37 + (decorated == null ? 0 : decorated.hashCode());
100        total = total*37 + (transformer == null ? 0 : transformer.hashCode());
101        return total;
102    }
103
104    /**
105     * Returns <code>true</code> iff <i>that</i> Object is
106     * is a {@link Comparator} whose ordering is known to be
107     * equivalent to mine.
108     * <p>
109     * This implementation returns <code>true</code>
110     * iff <code><i>that</i></code> is a {@link TransformingComparator}
111     * whose attributes are equal to mine.
112     *
113     * @param object  the object to compare to
114     * @return true if equal
115     */
116    @Override
117    public boolean equals(final Object object) {
118        if (this == object) {
119            return true;
120        }
121        if (null == object) {
122            return false;
123        }
124        if (object.getClass().equals(this.getClass())) {
125            final TransformingComparator<?, ?> comp = (TransformingComparator<?, ?>) object;
126            return (null == decorated ? null == comp.decorated : decorated.equals(comp.decorated)) &&
127                   (null == transformer ? null == comp.transformer : transformer.equals(comp.transformer));
128        }
129        return false;
130    }
131
132}
133