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 * <p>See the Guava User Guide article on <a href=
049 * "http://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained#compare/compareTo">
050 * {@code ComparisonChain}</a>.
051 *
052 * @author Mark Davis
053 * @author Kevin Bourrillion
054 * @since 2.0
055 */
056 @GwtCompatible
057 public abstract class ComparisonChain {
058 private ComparisonChain() {}
059
060 /**
061 * Begins a new chained comparison statement. See example in the class
062 * documentation.
063 */
064 public static ComparisonChain start() {
065 return ACTIVE;
066 }
067
068 private static final ComparisonChain ACTIVE = new ComparisonChain() {
069 @SuppressWarnings("unchecked")
070 @Override public ComparisonChain compare(
071 Comparable left, Comparable right) {
072 return classify(left.compareTo(right));
073 }
074 @Override public <T> ComparisonChain compare(
075 @Nullable T left, @Nullable T right, Comparator<T> comparator) {
076 return classify(comparator.compare(left, right));
077 }
078 @Override public ComparisonChain compare(int left, int right) {
079 return classify(Ints.compare(left, right));
080 }
081 @Override public ComparisonChain compare(long left, long right) {
082 return classify(Longs.compare(left, right));
083 }
084 @Override public ComparisonChain compare(float left, float right) {
085 return classify(Float.compare(left, right));
086 }
087 @Override public ComparisonChain compare(double left, double right) {
088 return classify(Double.compare(left, right));
089 }
090 @Override public ComparisonChain compareTrueFirst(boolean left, boolean right) {
091 return classify(Booleans.compare(right, left)); // reversed
092 }
093 @Override public ComparisonChain compareFalseFirst(boolean left, boolean right) {
094 return classify(Booleans.compare(left, right));
095 }
096 ComparisonChain classify(int result) {
097 return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
098 }
099 @Override public int result() {
100 return 0;
101 }
102 };
103
104 private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
105
106 private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
107
108 private static final class InactiveComparisonChain extends ComparisonChain {
109 final int result;
110
111 InactiveComparisonChain(int result) {
112 this.result = result;
113 }
114 @Override public ComparisonChain compare(
115 @Nullable Comparable left, @Nullable Comparable right) {
116 return this;
117 }
118 @Override public <T> ComparisonChain compare(@Nullable T left,
119 @Nullable T right, @Nullable Comparator<T> comparator) {
120 return this;
121 }
122 @Override public ComparisonChain compare(int left, int right) {
123 return this;
124 }
125 @Override public ComparisonChain compare(long left, long right) {
126 return this;
127 }
128 @Override public ComparisonChain compare(float left, float right) {
129 return this;
130 }
131 @Override public ComparisonChain compare(double left, double right) {
132 return this;
133 }
134 @Override public ComparisonChain compareTrueFirst(boolean left, boolean right) {
135 return this;
136 }
137 @Override public ComparisonChain compareFalseFirst(boolean left, boolean right) {
138 return this;
139 }
140 @Override public int result() {
141 return result;
142 }
143 }
144
145 /**
146 * Compares two comparable objects as specified by {@link
147 * Comparable#compareTo}, <i>if</i> the result of this comparison chain
148 * has not already been determined.
149 */
150 public abstract ComparisonChain compare(
151 Comparable<?> left, Comparable<?> right);
152
153 /**
154 * Compares two objects using a comparator, <i>if</i> the result of this
155 * comparison chain has not already been determined.
156 */
157 public abstract <T> ComparisonChain compare(
158 @Nullable T left, @Nullable T right, Comparator<T> comparator);
159
160 /**
161 * Compares two {@code int} values as specified by {@link Ints#compare},
162 * <i>if</i> the result of this comparison chain has not already been
163 * determined.
164 */
165 public abstract ComparisonChain compare(int left, int right);
166
167 /**
168 * Compares two {@code long} values as specified by {@link Longs#compare},
169 * <i>if</i> the result of this comparison chain has not already been
170 * determined.
171 */
172 public abstract ComparisonChain compare(long left, long right);
173
174 /**
175 * Compares two {@code float} values as specified by {@link
176 * Float#compare}, <i>if</i> the result of this comparison chain has not
177 * already been determined.
178 */
179 public abstract ComparisonChain compare(float left, float right);
180
181 /**
182 * Compares two {@code double} values as specified by {@link
183 * Double#compare}, <i>if</i> the result of this comparison chain has not
184 * already been determined.
185 */
186 public abstract ComparisonChain compare(double left, double right);
187
188 /**
189 * Compares two {@code boolean} values, considering {@code true} to be less
190 * than {@code false}, <i>if</i> the result of this comparison chain has not
191 * already been determined.
192 *
193 * @since 12.0
194 */
195 public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
196
197 /**
198 * Compares two {@code boolean} values, considering {@code false} to be less
199 * than {@code true}, <i>if</i> the result of this comparison chain has not
200 * already been determined.
201 *
202 * @since 12.0 (present as {@code compare} since 2.0)
203 */
204 public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
205
206 /**
207 * Old name of {@link #compareFalseFirst}.
208 *
209 * @deprecated Use {@link #compareFalseFirst}; or, if the parameters passed
210 * are being either negated or reversed, undo the negation or reversal and
211 * use {@link #compareTrueFirst}. <b>This method is scheduled for deletion
212 * in September 2013.</b>
213 */
214 @Deprecated
215 public final ComparisonChain compare(boolean left, boolean right) {
216 return compareFalseFirst(left, right);
217 }
218
219 /**
220 * Ends this comparison chain and returns its result: a value having the
221 * same sign as the first nonzero comparison result in the chain, or zero if
222 * every result was zero.
223 */
224 public abstract int result();
225 }