1 /*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.collect;
18
19 import com.google.common.annotations.GwtCompatible;
20 import com.google.common.primitives.Booleans;
21 import com.google.common.primitives.Ints;
22 import com.google.common.primitives.Longs;
23
24 import java.util.Comparator;
25
26 import javax.annotation.Nullable;
27
28 /**
29 * A utility for performing a chained comparison statement. For example:
30 * <pre> {@code
31 *
32 * public int compareTo(Foo that) {
33 * return ComparisonChain.start()
34 * .compare(this.aString, that.aString)
35 * .compare(this.anInt, that.anInt)
36 * .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
37 * .result();
38 * }}</pre>
39 *
40 * <p>The value of this expression will have the same sign as the <i>first
41 * nonzero</i> comparison result in the chain, or will be zero if every
42 * comparison result was zero.
43 *
44 * <p>Performance note: Even though the {@code ComparisonChain} caller always
45 * invokes its {@code compare} methods unconditionally, the {@code
46 * ComparisonChain} implementation stops calling its inputs' {@link
47 * Comparable#compareTo compareTo} and {@link Comparator#compare compare}
48 * methods as soon as one of them returns a nonzero result. This optimization is
49 * typically important only in the presence of expensive {@code compareTo} and
50 * {@code compare} implementations.
51 *
52 * <p>See the Guava User Guide article on <a href=
53 * "http://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained#compare/compareTo">
54 * {@code ComparisonChain}</a>.
55 *
56 * @author Mark Davis
57 * @author Kevin Bourrillion
58 * @since 2.0
59 */
60 @GwtCompatible
61 public abstract class ComparisonChain {
62 private ComparisonChain() {}
63
64 /**
65 * Begins a new chained comparison statement. See example in the class
66 * documentation.
67 */
68 public static ComparisonChain start() {
69 return ACTIVE;
70 }
71
72 private static final ComparisonChain ACTIVE = new ComparisonChain() {
73 @SuppressWarnings("unchecked")
74 @Override public ComparisonChain compare(
75 Comparable left, Comparable right) {
76 return classify(left.compareTo(right));
77 }
78 @Override public <T> ComparisonChain compare(
79 @Nullable T left, @Nullable T right, Comparator<T> comparator) {
80 return classify(comparator.compare(left, right));
81 }
82 @Override public ComparisonChain compare(int left, int right) {
83 return classify(Ints.compare(left, right));
84 }
85 @Override public ComparisonChain compare(long left, long right) {
86 return classify(Longs.compare(left, right));
87 }
88 @Override public ComparisonChain compare(float left, float right) {
89 return classify(Float.compare(left, right));
90 }
91 @Override public ComparisonChain compare(double left, double right) {
92 return classify(Double.compare(left, right));
93 }
94 @Override public ComparisonChain compareTrueFirst(boolean left, boolean right) {
95 return classify(Booleans.compare(right, left)); // reversed
96 }
97 @Override public ComparisonChain compareFalseFirst(boolean left, boolean right) {
98 return classify(Booleans.compare(left, right));
99 }
100 ComparisonChain classify(int result) {
101 return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
102 }
103 @Override public int result() {
104 return 0;
105 }
106 };
107
108 private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
109
110 private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
111
112 private static final class InactiveComparisonChain extends ComparisonChain {
113 final int result;
114
115 InactiveComparisonChain(int result) {
116 this.result = result;
117 }
118 @Override public ComparisonChain compare(
119 @Nullable Comparable left, @Nullable Comparable right) {
120 return this;
121 }
122 @Override public <T> ComparisonChain compare(@Nullable T left,
123 @Nullable T right, @Nullable Comparator<T> comparator) {
124 return this;
125 }
126 @Override public ComparisonChain compare(int left, int right) {
127 return this;
128 }
129 @Override public ComparisonChain compare(long left, long right) {
130 return this;
131 }
132 @Override public ComparisonChain compare(float left, float right) {
133 return this;
134 }
135 @Override public ComparisonChain compare(double left, double right) {
136 return this;
137 }
138 @Override public ComparisonChain compareTrueFirst(boolean left, boolean right) {
139 return this;
140 }
141 @Override public ComparisonChain compareFalseFirst(boolean left, boolean right) {
142 return this;
143 }
144 @Override public int result() {
145 return result;
146 }
147 }
148
149 /**
150 * Compares two comparable objects as specified by {@link
151 * Comparable#compareTo}, <i>if</i> the result of this comparison chain
152 * has not already been determined.
153 */
154 public abstract ComparisonChain compare(
155 Comparable<?> left, Comparable<?> right);
156
157 /**
158 * Compares two objects using a comparator, <i>if</i> the result of this
159 * comparison chain has not already been determined.
160 */
161 public abstract <T> ComparisonChain compare(
162 @Nullable T left, @Nullable T right, Comparator<T> comparator);
163
164 /**
165 * Compares two {@code int} values as specified by {@link Ints#compare},
166 * <i>if</i> the result of this comparison chain has not already been
167 * determined.
168 */
169 public abstract ComparisonChain compare(int left, int right);
170
171 /**
172 * Compares two {@code long} values as specified by {@link Longs#compare},
173 * <i>if</i> the result of this comparison chain has not already been
174 * determined.
175 */
176 public abstract ComparisonChain compare(long left, long right);
177
178 /**
179 * Compares two {@code float} values as specified by {@link
180 * Float#compare}, <i>if</i> the result of this comparison chain has not
181 * already been determined.
182 */
183 public abstract ComparisonChain compare(float left, float right);
184
185 /**
186 * Compares two {@code double} values as specified by {@link
187 * Double#compare}, <i>if</i> the result of this comparison chain has not
188 * already been determined.
189 */
190 public abstract ComparisonChain compare(double left, double right);
191
192 /**
193 * Compares two {@code boolean} values, considering {@code true} to be less
194 * than {@code false}, <i>if</i> the result of this comparison chain has not
195 * already been determined.
196 *
197 * @since 12.0
198 */
199 public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
200
201 /**
202 * Compares two {@code boolean} values, considering {@code false} to be less
203 * than {@code true}, <i>if</i> the result of this comparison chain has not
204 * already been determined.
205 *
206 * @since 12.0 (present as {@code compare} since 2.0)
207 */
208 public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
209
210 /**
211 * Ends this comparison chain and returns its result: a value having the
212 * same sign as the first nonzero comparison result in the chain, or zero if
213 * every result was zero.
214 */
215 public abstract int result();
216 }