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
017package com.google.common.collect;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.common.primitives.Booleans;
021import com.google.common.primitives.Ints;
022import com.google.common.primitives.Longs;
023import java.util.Comparator;
024import org.checkerframework.checker.nullness.qual.Nullable;
025
026/**
027 * A utility for performing a chained comparison statement. For example:
028 *
029 * <pre>{@code
030 * public int compareTo(Foo that) {
031 *   return ComparisonChain.start()
032 *       .compare(this.aString, that.aString)
033 *       .compare(this.anInt, that.anInt)
034 *       .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
035 *       .result();
036 * }
037 * }</pre>
038 *
039 * <p>The value of this expression will have the same sign as the <i>first nonzero</i> comparison
040 * result in the chain, or will be zero if every comparison result was zero.
041 *
042 * <p><b>Note:</b> {@code ComparisonChain} instances are <b>immutable</b>. For this utility to work
043 * correctly, calls must be chained as illustrated above.
044 *
045 * <p>Performance note: Even though the {@code ComparisonChain} caller always invokes its {@code
046 * compare} methods unconditionally, the {@code ComparisonChain} implementation stops calling its
047 * inputs' {@link Comparable#compareTo compareTo} and {@link Comparator#compare compare} methods as
048 * soon as one of them returns a nonzero result. This optimization is typically important only in
049 * the presence of expensive {@code compareTo} and {@code compare} implementations.
050 *
051 * <p>See the Guava User Guide article on <a href=
052 * "https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained#comparecompareto"> {@code
053 * ComparisonChain}</a>.
054 *
055 * @author Mark Davis
056 * @author Kevin Bourrillion
057 * @since 2.0
058 */
059@GwtCompatible
060@ElementTypesAreNonnullByDefault
061public abstract class ComparisonChain {
062  private ComparisonChain() {}
063
064  /** Begins a new chained comparison statement. See example in the class documentation. */
065  public static ComparisonChain start() {
066    return ACTIVE;
067  }
068
069  private static final ComparisonChain ACTIVE =
070      new ComparisonChain() {
071        @SuppressWarnings("unchecked") // unsafe; see discussion on supertype
072        @Override
073        public ComparisonChain compare(Comparable<?> left, Comparable<?> right) {
074          return classify(((Comparable<Object>) left).compareTo(right));
075        }
076
077        @Override
078        public <T extends @Nullable Object> ComparisonChain compare(
079            @ParametricNullness T left, @ParametricNullness T right, Comparator<T> comparator) {
080          return classify(comparator.compare(left, right));
081        }
082
083        @Override
084        public ComparisonChain compare(int left, int right) {
085          return classify(Ints.compare(left, right));
086        }
087
088        @Override
089        public ComparisonChain compare(long left, long right) {
090          return classify(Longs.compare(left, right));
091        }
092
093        @Override
094        public ComparisonChain compare(float left, float right) {
095          return classify(Float.compare(left, right));
096        }
097
098        @Override
099        public ComparisonChain compare(double left, double right) {
100          return classify(Double.compare(left, right));
101        }
102
103        @Override
104        public ComparisonChain compareTrueFirst(boolean left, boolean right) {
105          return classify(Booleans.compare(right, left)); // reversed
106        }
107
108        @Override
109        public ComparisonChain compareFalseFirst(boolean left, boolean right) {
110          return classify(Booleans.compare(left, right));
111        }
112
113        ComparisonChain classify(int result) {
114          return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
115        }
116
117        @Override
118        public int result() {
119          return 0;
120        }
121      };
122
123  private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
124
125  private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
126
127  private static final class InactiveComparisonChain extends ComparisonChain {
128    final int result;
129
130    InactiveComparisonChain(int result) {
131      this.result = result;
132    }
133
134    @Override
135    public ComparisonChain compare(Comparable<?> left, Comparable<?> right) {
136      return this;
137    }
138
139    @Override
140    public <T extends @Nullable Object> ComparisonChain compare(
141        @ParametricNullness T left, @ParametricNullness T right, Comparator<T> comparator) {
142      return this;
143    }
144
145    @Override
146    public ComparisonChain compare(int left, int right) {
147      return this;
148    }
149
150    @Override
151    public ComparisonChain compare(long left, long right) {
152      return this;
153    }
154
155    @Override
156    public ComparisonChain compare(float left, float right) {
157      return this;
158    }
159
160    @Override
161    public ComparisonChain compare(double left, double right) {
162      return this;
163    }
164
165    @Override
166    public ComparisonChain compareTrueFirst(boolean left, boolean right) {
167      return this;
168    }
169
170    @Override
171    public ComparisonChain compareFalseFirst(boolean left, boolean right) {
172      return this;
173    }
174
175    @Override
176    public int result() {
177      return result;
178    }
179  }
180
181  /**
182   * Compares two comparable objects as specified by {@link Comparable#compareTo}, <i>if</i> the
183   * result of this comparison chain has not already been determined.
184   *
185   * <p>This method is declared to accept any 2 {@code Comparable} objects, even if they are not <a
186   * href="https://docs.oracle.com/javase/tutorial/collections/interfaces/order.html">mutually
187   * comparable</a>. If you pass objects that are not mutually comparable, this method may throw an
188   * exception. (The reason for this decision is lost to time, but the reason <i>might</i> be that
189   * we wanted to support legacy classes that implement the raw type {@code Comparable} (instead of
190   * implementing {@code Comparable<Foo>}) without producing warnings. If so, we would prefer today
191   * to produce warnings in that case, and we may change this method to do so in the future. Support
192   * for raw {@code Comparable} types in Guava in general is tracked as <a
193   * href="https://github.com/google/guava/issues/989">#989</a>.)
194   *
195   * @throws ClassCastException if the parameters are not mutually comparable
196   */
197  public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right);
198
199  /**
200   * Compares two objects using a comparator, <i>if</i> the result of this comparison chain has not
201   * already been determined.
202   */
203  public abstract <T extends @Nullable Object> ComparisonChain compare(
204      @ParametricNullness T left, @ParametricNullness T right, Comparator<T> comparator);
205
206  /**
207   * Compares two {@code int} values as specified by {@link Ints#compare}, <i>if</i> the result of
208   * this comparison chain has not already been determined.
209   */
210  public abstract ComparisonChain compare(int left, int right);
211
212  /**
213   * Compares two {@code long} values as specified by {@link Longs#compare}, <i>if</i> the result of
214   * this comparison chain has not already been determined.
215   */
216  public abstract ComparisonChain compare(long left, long right);
217
218  /**
219   * Compares two {@code float} values as specified by {@link Float#compare}, <i>if</i> the result
220   * of this comparison chain has not already been determined.
221   */
222  public abstract ComparisonChain compare(float left, float right);
223
224  /**
225   * Compares two {@code double} values as specified by {@link Double#compare}, <i>if</i> the result
226   * of this comparison chain has not already been determined.
227   */
228  public abstract ComparisonChain compare(double left, double right);
229
230  /**
231   * Discouraged synonym for {@link #compareFalseFirst}.
232   *
233   * @deprecated Use {@link #compareFalseFirst}; or, if the parameters passed are being either
234   *     negated or reversed, undo the negation or reversal and use {@link #compareTrueFirst}.
235   * @since 19.0
236   */
237  @Deprecated
238  public final ComparisonChain compare(Boolean left, Boolean right) {
239    return compareFalseFirst(left, right);
240  }
241
242  /**
243   * Compares two {@code boolean} values, considering {@code true} to be less than {@code false},
244   * <i>if</i> the result of this comparison chain has not already been determined.
245   *
246   * @since 12.0
247   */
248  public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
249
250  /**
251   * Compares two {@code boolean} values, considering {@code false} to be less than {@code true},
252   * <i>if</i> the result of this comparison chain has not already been determined.
253   *
254   * @since 12.0 (present as {@code compare} since 2.0)
255   */
256  public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
257
258  /**
259   * Ends this comparison chain and returns its result: a value having the same sign as the first
260   * nonzero comparison result in the chain, or zero if every result was zero.
261   */
262  public abstract int result();
263}