    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