001/*
002 * Copyright 2002-2012 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.util.comparator;
018
019import java.io.Serializable;
020import java.util.Comparator;
021
022import org.springframework.util.Assert;
023
024/**
025 * A decorator for a comparator, with an "ascending" flag denoting
026 * whether comparison results should be treated in forward (standard
027 * ascending) order or flipped for reverse (descending) order.
028 *
029 * @author Keith Donald
030 * @author Juergen Hoeller
031 * @since 1.2.2
032 */
033@SuppressWarnings("serial")
034public class InvertibleComparator<T> implements Comparator<T>, Serializable {
035
036        private final Comparator<T> comparator;
037
038        private boolean ascending = true;
039
040
041        /**
042         * Create an InvertibleComparator that sorts ascending by default.
043         * For the actual comparison, the specified Comparator will be used.
044         * @param comparator the comparator to decorate
045         */
046        public InvertibleComparator(Comparator<T> comparator) {
047                Assert.notNull(comparator, "Comparator must not be null");
048                this.comparator = comparator;
049        }
050
051        /**
052         * Create an InvertibleComparator that sorts based on the provided order.
053         * For the actual comparison, the specified Comparator will be used.
054         * @param comparator the comparator to decorate
055         * @param ascending the sort order: ascending (true) or descending (false)
056         */
057        public InvertibleComparator(Comparator<T> comparator, boolean ascending) {
058                Assert.notNull(comparator, "Comparator must not be null");
059                this.comparator = comparator;
060                setAscending(ascending);
061        }
062
063
064        /**
065         * Specify the sort order: ascending (true) or descending (false).
066         */
067        public void setAscending(boolean ascending) {
068                this.ascending = ascending;
069        }
070
071        /**
072         * Return the sort order: ascending (true) or descending (false).
073         */
074        public boolean isAscending() {
075                return this.ascending;
076        }
077
078        /**
079         * Invert the sort order: ascending -> descending or
080         * descending -> ascending.
081         */
082        public void invertOrder() {
083                this.ascending = !this.ascending;
084        }
085
086
087        @Override
088        public int compare(T o1, T o2) {
089                int result = this.comparator.compare(o1, o2);
090                if (result != 0) {
091                        // Invert the order if it is a reverse sort.
092                        if (!this.ascending) {
093                                if (Integer.MIN_VALUE == result) {
094                                        result = Integer.MAX_VALUE;
095                                }
096                                else {
097                                        result *= -1;
098                                }
099                        }
100                        return result;
101                }
102                return 0;
103        }
104
105        @Override
106        @SuppressWarnings("unchecked")
107        public boolean equals(Object obj) {
108                if (this == obj) {
109                        return true;
110                }
111                if (!(obj instanceof InvertibleComparator)) {
112                        return false;
113                }
114                InvertibleComparator<T> other = (InvertibleComparator<T>) obj;
115                return (this.comparator.equals(other.comparator) && this.ascending == other.ascending);
116        }
117
118        @Override
119        public int hashCode() {
120                return this.comparator.hashCode();
121        }
122
123        @Override
124        public String toString() {
125                return "InvertibleComparator: [" + this.comparator + "]; ascending=" + this.ascending;
126        }
127
128}