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;
021import java.util.Objects;
022
023import org.apache.commons.collections4.ComparatorUtils;
024import org.apache.commons.collections4.Transformer;
025
026/**
027 * Decorates another Comparator with transformation behavior. That is, the
028 * return value from the transform operation will be passed to the decorated
029 * {@link Comparator#compare(Object,Object) compare} method.
030 * <p>
031 * This class is Serializable from Commons Collections 4.0.
032 * </p>
033 *
034 * @param <I> the input type to the transformer
035 * @param <O> the output type from the transformer
036 *
037 * @since 2.1
038 *
039 * @see org.apache.commons.collections4.Transformer
040 * @see org.apache.commons.collections4.comparators.ComparableComparator
041 */
042public class TransformingComparator<I, O> implements Comparator<I>, Serializable {
043
044    /** Serialization version from Collections 4.0. */
045    private static final long serialVersionUID = 3456940356043606220L;
046
047    /** The decorated comparator. */
048    private final Comparator<O> decorated;
049
050    /** The transformer being used. */
051    private final Transformer<? super I, ? extends O> transformer;
052
053    /**
054     * Constructs an instance with the given Transformer and a
055     * {@link ComparableComparator ComparableComparator}.
056     *
057     * @param transformer what will transform the arguments to {@code compare}
058     */
059    public TransformingComparator(final Transformer<? super I, ? extends O> transformer) {
060        this(transformer, ComparatorUtils.NATURAL_COMPARATOR);
061    }
062
063    /**
064     * Constructs an instance with the given Transformer and Comparator.
065     *
066     * @param transformer  what will transform the arguments to {@code compare}
067     * @param decorated  the decorated Comparator
068     */
069    public TransformingComparator(final Transformer<? super I, ? extends O> transformer,
070                                  final Comparator<O> decorated) {
071        this.decorated = decorated;
072        this.transformer = transformer;
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     * Returns {@code true} iff <i>that</i> Object is
091     * a {@link Comparator} whose ordering is known to be
092     * equivalent to mine.
093     * <p>
094     * This implementation returns {@code true}
095     * iff {@code <i>that</i>} is a {@link TransformingComparator}
096     * whose attributes are equal to mine.
097     *
098     * @param object  the object to compare to
099     * @return true if equal
100     */
101    @Override
102    public boolean equals(final Object object) {
103        if (this == object) {
104            return true;
105        }
106        if (null == object) {
107            return false;
108        }
109        if (object.getClass().equals(this.getClass())) {
110            final TransformingComparator<?, ?> comp = (TransformingComparator<?, ?>) object;
111            return Objects.equals(decorated, comp.decorated) &&
112                   Objects.equals(transformer, comp.transformer);
113        }
114        return false;
115    }
116
117    /**
118     * Implement a hash code for this comparator that is consistent with
119     * {@link #equals(Object) equals}.
120     *
121     * @return a hash code for this comparator.
122     */
123    @Override
124    public int hashCode() {
125        int total = 17;
126        total = total * 37 + (decorated == null ? 0 : decorated.hashCode());
127        return total * 37 + (transformer == null ? 0 : transformer.hashCode());
128    }
129
130}
131