001/* 002 * Copyright 2009-2014 UnboundID Corp. 003 * All Rights Reserved. 004 */ 005/* 006 * Copyright (C) 2009-2014 UnboundID Corp. 007 * 008 * This program is free software; you can redistribute it and/or modify 009 * it under the terms of the GNU General Public License (GPLv2 only) 010 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only) 011 * as published by the Free Software Foundation. 012 * 013 * This program is distributed in the hope that it will be useful, 014 * but WITHOUT ANY WARRANTY; without even the implied warranty of 015 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 016 * GNU General Public License for more details. 017 * 018 * You should have received a copy of the GNU General Public License 019 * along with this program; if not, see <http://www.gnu.org/licenses>. 020 */ 021package com.unboundid.util; 022 023 024 025import java.io.Serializable; 026import java.util.Comparator; 027 028 029 030/** 031 * This class provides an implementation of a {@code Comparator} object that may 032 * be used to iterate through values in what would normally be considered 033 * reverse order. 034 * 035 * @param <T> The type of object to use with this comparator. 036 */ 037@NotMutable() 038@ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE) 039public final class ReverseComparator<T> 040 implements Comparator<T>, Serializable 041{ 042 /** 043 * The serial version UID for this serializable class. 044 */ 045 private static final long serialVersionUID = -4615537960027681276L; 046 047 048 049 // The comparator that will be used to make the underlying determination. 050 private final Comparator<T> baseComparator; 051 052 053 054 /** 055 * Creates a new comparator that will sort items in reverse order. The 056 * generic type for this class must implement the {@link Comparable} 057 * interface. 058 */ 059 public ReverseComparator() 060 { 061 baseComparator = null; 062 } 063 064 065 066 /** 067 * Creates a new comparator that will sort items in the reverse order that 068 * they would be normally sorted using the given comparator. 069 * 070 * @param baseComparator The base comparator that will be used to make the 071 * determination. 072 */ 073 public ReverseComparator(final Comparator<T> baseComparator) 074 { 075 this.baseComparator = baseComparator; 076 } 077 078 079 080 /** 081 * Compares the provided objects to determine their relative order in a 082 * sorted list. 083 * 084 * @param o1 The first object to compare. 085 * @param o2 The second object to compare. 086 * 087 * @return A negative integer if the first object should be ordered before 088 * the second, a positive integer if the first object should be 089 * ordered after the second, or zero if there is no difference in 090 * their relative orders. 091 */ 092 @SuppressWarnings("unchecked") 093 public int compare(final T o1, final T o2) 094 { 095 final int baseValue; 096 if (baseComparator == null) 097 { 098 baseValue = ((Comparable<? super T>) o1).compareTo(o2); 099 } 100 else 101 { 102 baseValue = baseComparator.compare(o1, o2); 103 } 104 105 if (baseValue < 0) 106 { 107 return 1; 108 } 109 else if (baseValue > 0) 110 { 111 return -1; 112 } 113 else 114 { 115 return 0; 116 } 117 } 118 119 120 121 /** 122 * Retrieves a hash code for this class. 123 * 124 * @return A hash code for this class. 125 */ 126 @Override() 127 public int hashCode() 128 { 129 if (baseComparator == null) 130 { 131 return 0; 132 } 133 else 134 { 135 return baseComparator.hashCode(); 136 } 137 } 138 139 140 141 /** 142 * Indicates whether the provided object may be considered equal to this 143 * comparator. 144 * 145 * @param o The object for which to make the determination. 146 * 147 * @return {@code true} if the provided object may be considered equal to 148 * this comparator, or {@code false} if not. 149 */ 150 @Override() 151 @SuppressWarnings("unchecked") 152 public boolean equals(final Object o) 153 { 154 if (o == null) 155 { 156 return false; 157 } 158 159 if (o == this) 160 { 161 return true; 162 } 163 164 if (! (o.getClass().equals(ReverseComparator.class))) 165 { 166 return false; 167 } 168 169 final ReverseComparator<T> c = (ReverseComparator<T>) o; 170 if (baseComparator == null) 171 { 172 return (c.baseComparator == null); 173 } 174 else 175 { 176 return baseComparator.equals(c.baseComparator); 177 } 178 } 179}