001/* 002 * Copyright 2009-2019 Ping Identity Corporation 003 * All Rights Reserved. 004 */ 005/* 006 * Copyright (C) 2009-2019 Ping Identity Corporation 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 @Override() 094 public int compare(final T o1, final T o2) 095 { 096 final int baseValue; 097 if (baseComparator == null) 098 { 099 baseValue = ((Comparable<? super T>) o1).compareTo(o2); 100 } 101 else 102 { 103 baseValue = baseComparator.compare(o1, o2); 104 } 105 106 if (baseValue < 0) 107 { 108 return 1; 109 } 110 else if (baseValue > 0) 111 { 112 return -1; 113 } 114 else 115 { 116 return 0; 117 } 118 } 119 120 121 122 /** 123 * Retrieves a hash code for this class. 124 * 125 * @return A hash code for this class. 126 */ 127 @Override() 128 public int hashCode() 129 { 130 if (baseComparator == null) 131 { 132 return 0; 133 } 134 else 135 { 136 return baseComparator.hashCode(); 137 } 138 } 139 140 141 142 /** 143 * Indicates whether the provided object may be considered equal to this 144 * comparator. 145 * 146 * @param o The object for which to make the determination. 147 * 148 * @return {@code true} if the provided object may be considered equal to 149 * this comparator, or {@code false} if not. 150 */ 151 @Override() 152 @SuppressWarnings("unchecked") 153 public boolean equals(final Object o) 154 { 155 if (o == null) 156 { 157 return false; 158 } 159 160 if (o == this) 161 { 162 return true; 163 } 164 165 if (! (o.getClass().equals(ReverseComparator.class))) 166 { 167 return false; 168 } 169 170 final ReverseComparator<T> c = (ReverseComparator<T>) o; 171 if (baseComparator == null) 172 { 173 return (c.baseComparator == null); 174 } 175 else 176 { 177 return baseComparator.equals(c.baseComparator); 178 } 179 } 180}