001 /*
002 * Copyright (C) 2009 The Guava 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 * http://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
017 package com.google.common.collect;
018
019 import com.google.common.annotations.GwtCompatible;
020 import com.google.common.primitives.Booleans;
021 import com.google.common.primitives.Ints;
022 import com.google.common.primitives.Longs;
023
024 import java.util.Comparator;
025
026 import javax.annotation.Nullable;
027
028 /**
029 * A utility for performing a "lazy" chained comparison statement, which
030 * performs comparisons only until it finds a nonzero result. For example:
031 * <pre> {@code
032 *
033 * public int compareTo(Foo that) {
034 * return ComparisonChain.start()
035 * .compare(this.aString, that.aString)
036 * .compare(this.anInt, that.anInt)
037 * .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
038 * .result();
039 * }}</pre>
040 *
041 * The value of this expression will have the same sign as the <i>first
042 * nonzero</i> comparison result in the chain, or will be zero if every
043 * comparison result was zero.
044 *
045 * <p>Once any comparison returns a nonzero value, remaining comparisons are
046 * "short-circuited".
047 *
048 * @author Mark Davis
049 * @author Kevin Bourrillion
050 * @since 2.0
051 */
052 @GwtCompatible
053 public abstract class ComparisonChain {
054 private ComparisonChain() {}
055
056 /**
057 * Begins a new chained comparison statement. See example in the class
058 * documentation.
059 */
060 public static ComparisonChain start() {
061 return ACTIVE;
062 }
063
064 private static final ComparisonChain ACTIVE = new ComparisonChain() {
065 @SuppressWarnings("unchecked")
066 @Override public ComparisonChain compare(
067 Comparable left, Comparable right) {
068 return classify(left.compareTo(right));
069 }
070 @Override public <T> ComparisonChain compare(
071 @Nullable T left, @Nullable T right, Comparator<T> comparator) {
072 return classify(comparator.compare(left, right));
073 }
074 @Override public ComparisonChain compare(int left, int right) {
075 return classify(Ints.compare(left, right));
076 }
077 @Override public ComparisonChain compare(long left, long right) {
078 return classify(Longs.compare(left, right));
079 }
080 @Override public ComparisonChain compare(float left, float right) {
081 return classify(Float.compare(left, right));
082 }
083 @Override public ComparisonChain compare(double left, double right) {
084 return classify(Double.compare(left, right));
085 }
086 @Override public ComparisonChain compare(boolean left, boolean right) {
087 return classify(Booleans.compare(left, right));
088 }
089 ComparisonChain classify(int result) {
090 return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
091 }
092 @Override public int result() {
093 return 0;
094 }
095 };
096
097 private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
098
099 private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
100
101 private static final class InactiveComparisonChain extends ComparisonChain {
102 final int result;
103
104 InactiveComparisonChain(int result) {
105 this.result = result;
106 }
107 @Override public ComparisonChain compare(
108 @Nullable Comparable left, @Nullable Comparable right) {
109 return this;
110 }
111 @Override public <T> ComparisonChain compare(@Nullable T left,
112 @Nullable T right, @Nullable Comparator<T> comparator) {
113 return this;
114 }
115 @Override public ComparisonChain compare(int left, int right) {
116 return this;
117 }
118 @Override public ComparisonChain compare(long left, long right) {
119 return this;
120 }
121 @Override public ComparisonChain compare(float left, float right) {
122 return this;
123 }
124 @Override public ComparisonChain compare(double left, double right) {
125 return this;
126 }
127 @Override public ComparisonChain compare(boolean left, boolean right) {
128 return this;
129 }
130 @Override public int result() {
131 return result;
132 }
133 }
134
135 /**
136 * Compares two comparable objects as specified by {@link
137 * Comparable#compareTo}, <i>if</i> the result of this comparison chain
138 * has not already been determined.
139 */
140 public abstract ComparisonChain compare(
141 Comparable<?> left, Comparable<?> right);
142
143 /**
144 * Compares two objects using a comparator, <i>if</i> the result of this
145 * comparison chain has not already been determined.
146 */
147 public abstract <T> ComparisonChain compare(
148 @Nullable T left, @Nullable T right, Comparator<T> comparator);
149
150 /**
151 * Compares two {@code int} values as specified by {@link Ints#compare},
152 * <i>if</i> the result of this comparison chain has not already been
153 * determined.
154 */
155 public abstract ComparisonChain compare(int left, int right);
156
157 /**
158 * Compares two {@code long} values as specified by {@link Longs#compare},
159 * <i>if</i> the result of this comparison chain has not already been
160 * determined.
161 */
162 public abstract ComparisonChain compare(long left, long right);
163
164 /**
165 * Compares two {@code float} values as specified by {@link
166 * Float#compare}, <i>if</i> the result of this comparison chain has not
167 * already been determined.
168 */
169 public abstract ComparisonChain compare(float left, float right);
170
171 /**
172 * Compares two {@code double} values as specified by {@link
173 * Double#compare}, <i>if</i> the result of this comparison chain has not
174 * already been determined.
175 */
176 public abstract ComparisonChain compare(double left, double right);
177
178 /**
179 * Compares two {@code boolean} values as specified by {@link
180 * Booleans#compare}, <i>if</i> the result of this comparison chain has not
181 * already been determined.
182 */
183 public abstract ComparisonChain compare(boolean left, boolean right);
184
185 /**
186 * Ends this comparison chain and returns its result: a value having the
187 * same sign as the first nonzero comparison result in the chain, or zero if
188 * every result was zero.
189 */
190 public abstract int result();
191 }