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
060public abstract class ComparisonChain {
061  private ComparisonChain() {}
062
063  /** Begins a new chained comparison statement. See example in the class documentation. */
064  public static ComparisonChain start() {
065    return ACTIVE;
066  }
067
068  private static final ComparisonChain ACTIVE =
069      new ComparisonChain() {
070        @SuppressWarnings("unchecked")
071        @Override
072        public ComparisonChain compare(Comparable left, Comparable right) {
073          return classify(left.compareTo(right));
074        }
075
076        @Override
077        public <T> ComparisonChain compare(
078            @Nullable T left, @Nullable T right, Comparator<T> comparator) {
079          return classify(comparator.compare(left, right));
080        }
081
082        @Override
083        public ComparisonChain compare(int left, int right) {
084          return classify(Ints.compare(left, right));
085        }
086
087        @Override
088        public ComparisonChain compare(long left, long right) {
089          return classify(Longs.compare(left, right));
090        }
091
092        @Override
093        public ComparisonChain compare(float left, float right) {
094          return classify(Float.compare(left, right));
095        }
096
097        @Override
098        public ComparisonChain compare(double left, double right) {
099          return classify(Double.compare(left, right));
100        }
101
102        @Override
103        public ComparisonChain compareTrueFirst(boolean left, boolean right) {
104          return classify(Booleans.compare(right, left)); // reversed
105        }
106
107        @Override
108        public ComparisonChain compareFalseFirst(boolean left, boolean right) {
109          return classify(Booleans.compare(left, right));
110        }
111
112        ComparisonChain classify(int result) {
113          return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
114        }
115
116        @Override
117        public int result() {
118          return 0;
119        }
120      };
121
122  private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
123
124  private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
125
126  private static final class InactiveComparisonChain extends ComparisonChain {
127    final int result;
128
129    InactiveComparisonChain(int result) {
130      this.result = result;
131    }
132
133    @Override
134    public ComparisonChain compare(@Nullable Comparable left, @Nullable Comparable right) {
135      return this;
136    }
137
138    @Override
139    public <T> ComparisonChain compare(
140        @Nullable T left, @Nullable T right, @Nullable Comparator<T> comparator) {
141      return this;
142    }
143
144    @Override
145    public ComparisonChain compare(int left, int right) {
146      return this;
147    }
148
149    @Override
150    public ComparisonChain compare(long left, long right) {
151      return this;
152    }
153
154    @Override
155    public ComparisonChain compare(float left, float right) {
156      return this;
157    }
158
159    @Override
160    public ComparisonChain compare(double left, double right) {
161      return this;
162    }
163
164    @Override
165    public ComparisonChain compareTrueFirst(boolean left, boolean right) {
166      return this;
167    }
168
169    @Override
170    public ComparisonChain compareFalseFirst(boolean left, boolean right) {
171      return this;
172    }
173
174    @Override
175    public int result() {
176      return result;
177    }
178  }
179
180  /**
181   * Compares two comparable objects as specified by {@link Comparable#compareTo}, <i>if</i> the
182   * result of this comparison chain has not already been determined.
183   */
184  public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right);
185
186  /**
187   * Compares two objects using a comparator, <i>if</i> the result of this comparison chain has not
188   * already been determined.
189   */
190  public abstract <T> ComparisonChain compare(
191      @Nullable T left, @Nullable T right, Comparator<T> comparator);
192
193  /**
194   * Compares two {@code int} values as specified by {@link Ints#compare}, <i>if</i> the result of
195   * this comparison chain has not already been determined.
196   */
197  public abstract ComparisonChain compare(int left, int right);
198
199  /**
200   * Compares two {@code long} values as specified by {@link Longs#compare}, <i>if</i> the result of
201   * this comparison chain has not already been determined.
202   */
203  public abstract ComparisonChain compare(long left, long right);
204
205  /**
206   * Compares two {@code float} values as specified by {@link Float#compare}, <i>if</i> the result
207   * of this comparison chain has not already been determined.
208   */
209  public abstract ComparisonChain compare(float left, float right);
210
211  /**
212   * Compares two {@code double} values as specified by {@link Double#compare}, <i>if</i> the result
213   * of this comparison chain has not already been determined.
214   */
215  public abstract ComparisonChain compare(double left, double right);
216
217  /**
218   * Discouraged synonym for {@link #compareFalseFirst}.
219   *
220   * @deprecated Use {@link #compareFalseFirst}; or, if the parameters passed are being either
221   *     negated or reversed, undo the negation or reversal and use {@link #compareTrueFirst}.
222   * @since 19.0
223   */
224  @Deprecated
225  public final ComparisonChain compare(Boolean left, Boolean right) {
226    return compareFalseFirst(left, right);
227  }
228
229  /**
230   * Compares two {@code boolean} values, considering {@code true} to be less than {@code false},
231   * <i>if</i> the result of this comparison chain has not already been determined.
232   *
233   * @since 12.0
234   */
235  public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
236
237  /**
238   * Compares two {@code boolean} values, considering {@code false} to be less than {@code true},
239   * <i>if</i> the result of this comparison chain has not already been determined.
240   *
241   * @since 12.0 (present as {@code compare} since 2.0)
242   */
243  public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
244
245  /**
246   * Ends this comparison chain and returns its result: a value having the same sign as the first
247   * nonzero comparison result in the chain, or zero if every result was zero.
248   */
249  public abstract int result();
250}