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