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 /** The transformer being used. */ 050 private final Transformer<? super I, ? extends O> transformer; 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} 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} 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 * Returns the result of comparing the values from the transform operation. 076 * 077 * @param obj1 the first object to transform then compare 078 * @param obj2 the second object to transform then compare 079 * @return negative if obj1 is less, positive if greater, zero if equal 080 */ 081 @Override 082 public int compare(final I obj1, final I obj2) { 083 final O value1 = this.transformer.transform(obj1); 084 final O value2 = this.transformer.transform(obj2); 085 return this.decorated.compare(value1, value2); 086 } 087 088 /** 089 * Returns {@code true} iff <i>that</i> Object is 090 * a {@link Comparator} whose ordering is known to be 091 * equivalent to mine. 092 * <p> 093 * This implementation returns {@code true} 094 * iff {@code <i>that</i>} is a {@link TransformingComparator} 095 * whose attributes are equal to mine. 096 * 097 * @param object the object to compare to 098 * @return true if equal 099 */ 100 @Override 101 public boolean equals(final Object object) { 102 if (this == object) { 103 return true; 104 } 105 if (null == object) { 106 return false; 107 } 108 if (object.getClass().equals(this.getClass())) { 109 final TransformingComparator<?, ?> comp = (TransformingComparator<?, ?>) object; 110 return Objects.equals(decorated, comp.decorated) && 111 Objects.equals(transformer, comp.transformer); 112 } 113 return false; 114 } 115 116 /** 117 * Implement a hash code for this comparator that is consistent with 118 * {@link #equals(Object) equals}. 119 * 120 * @return a hash code for this comparator. 121 */ 122 @Override 123 public int hashCode() { 124 int total = 17; 125 total = total*37 + (decorated == null ? 0 : decorated.hashCode()); 126 total = total*37 + (transformer == null ? 0 : transformer.hashCode()); 127 return total; 128 } 129 130} 131