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 * 032 * @since 2.1 033 * @version $Id: TransformingComparator.html 972421 2015-11-14 20:00:04Z tn $ 034 * 035 * @see org.apache.commons.collections4.Transformer 036 * @see org.apache.commons.collections4.comparators.ComparableComparator 037 */ 038public class TransformingComparator<I, O> implements Comparator<I>, Serializable { 039 040 /** Serialization version from Collections 4.0. */ 041 private static final long serialVersionUID = 3456940356043606220L; 042 043 /** The decorated comparator. */ 044 private final Comparator<O> decorated; 045 /** The transformer being used. */ 046 private final Transformer<? super I, ? extends O> transformer; 047 048 //----------------------------------------------------------------------- 049 /** 050 * Constructs an instance with the given Transformer and a 051 * {@link ComparableComparator ComparableComparator}. 052 * 053 * @param transformer what will transform the arguments to <code>compare</code> 054 */ 055 @SuppressWarnings("unchecked") 056 public TransformingComparator(final Transformer<? super I, ? extends O> transformer) { 057 this(transformer, ComparatorUtils.NATURAL_COMPARATOR); 058 } 059 060 /** 061 * Constructs an instance with the given Transformer and Comparator. 062 * 063 * @param transformer what will transform the arguments to <code>compare</code> 064 * @param decorated the decorated Comparator 065 */ 066 public TransformingComparator(final Transformer<? super I, ? extends O> transformer, 067 final Comparator<O> decorated) { 068 this.decorated = decorated; 069 this.transformer = transformer; 070 } 071 072 //----------------------------------------------------------------------- 073 /** 074 * Returns the result of comparing the values from the transform operation. 075 * 076 * @param obj1 the first object to transform then compare 077 * @param obj2 the second object to transform then compare 078 * @return negative if obj1 is less, positive if greater, zero if equal 079 */ 080 public int compare(final I obj1, final I obj2) { 081 final O value1 = this.transformer.transform(obj1); 082 final O value2 = this.transformer.transform(obj2); 083 return this.decorated.compare(value1, value2); 084 } 085 086 //----------------------------------------------------------------------- 087 /** 088 * Implement a hash code for this comparator that is consistent with 089 * {@link #equals(Object) equals}. 090 * 091 * @return a hash code for this comparator. 092 */ 093 @Override 094 public int hashCode() { 095 int total = 17; 096 total = total*37 + (decorated == null ? 0 : decorated.hashCode()); 097 total = total*37 + (transformer == null ? 0 : transformer.hashCode()); 098 return total; 099 } 100 101 /** 102 * Returns <code>true</code> iff <i>that</i> Object is 103 * is a {@link Comparator} whose ordering is known to be 104 * equivalent to mine. 105 * <p> 106 * This implementation returns <code>true</code> 107 * iff <code><i>that</i></code> is a {@link TransformingComparator} 108 * whose attributes are equal to mine. 109 * 110 * @param object the object to compare to 111 * @return true if equal 112 */ 113 @Override 114 public boolean equals(final Object object) { 115 if (this == object) { 116 return true; 117 } 118 if (null == object) { 119 return false; 120 } 121 if (object.getClass().equals(this.getClass())) { 122 final TransformingComparator<?, ?> comp = (TransformingComparator<?, ?>) object; 123 return null == decorated ? null == comp.decorated : decorated.equals(comp.decorated) && 124 null == transformer ? null == comp.transformer : transformer.equals(comp.transformer); 125 } 126 return false; 127 } 128 129} 130