    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