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Java example source code file (ComparisonChain.java)

This example Java source code file (ComparisonChain.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, boolean, comparable, comparator, comparisonchain, deprecated, greater, gwtcompatible, inactivecomparisonchain, less, nullable, override, suppresswarnings, util

The ComparisonChain.java Java example source code

/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.primitives.Booleans;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;

import java.util.Comparator;

import javax.annotation.Nullable;

/**
 * A utility for performing a chained comparison statement. For example:
 * <pre>   {@code
 *
 *   public int compareTo(Foo that) {
 *     return ComparisonChain.start()
 *         .compare(this.aString, that.aString)
 *         .compare(this.anInt, that.anInt)
 *         .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
 *         .result();
 *   }}</pre>
 *
 * <p>The value of this expression will have the same sign as the first
 * nonzero</i> comparison result in the chain, or will be zero if every
 * comparison result was zero.
 *
 * <p>Note: {@code ComparisonChain} instances are immutable. For
 * this utility to work correctly, calls must be chained as illustrated above.
 *
 * <p>Performance note: Even though the {@code ComparisonChain} caller always
 * invokes its {@code compare} methods unconditionally, the {@code
 * ComparisonChain} implementation stops calling its inputs' {@link
 * Comparable#compareTo compareTo} and {@link Comparator#compare compare}
 * methods as soon as one of them returns a nonzero result. This optimization is
 * typically important only in the presence of expensive {@code compareTo} and
 * {@code compare} implementations.
 *
 * <p>See the Guava User Guide article on  the result of this comparison chain
   * has not already been determined.
   */
  public abstract ComparisonChain compare(Comparable<?> left, Comparable right);

  /**
   * Compares two objects using a comparator, <i>if the result of this
   * comparison chain has not already been determined.
   */
  public abstract <T> ComparisonChain compare(
      @Nullable T left, @Nullable T right, Comparator<T> comparator);

  /**
   * Compares two {@code int} values as specified by {@link Ints#compare},
   * <i>if the result of this comparison chain has not already been
   * determined.
   */
  public abstract ComparisonChain compare(int left, int right);

  /**
   * Compares two {@code long} values as specified by {@link Longs#compare},
   * <i>if the result of this comparison chain has not already been
   * determined.
   */
  public abstract ComparisonChain compare(long left, long right);

  /**
   * Compares two {@code float} values as specified by {@link
   * Float#compare}, <i>if the result of this comparison chain has not
   * already been determined.
   */
  public abstract ComparisonChain compare(float left, float right);

  /**
   * Compares two {@code double} values as specified by {@link
   * Double#compare}, <i>if the result of this comparison chain has not
   * already been determined.
   */
  public abstract ComparisonChain compare(double left, double right);

  /**
   * Discouraged synonym for {@link #compareFalseFirst}.
   *
   * @deprecated Use {@link #compareFalseFirst}; or, if the parameters passed
   *     are being either negated or reversed, undo the negation or reversal and
   *     use {@link #compareTrueFirst}.
   * @since 19.0
   */
  @Deprecated
  public final ComparisonChain compare(Boolean left, Boolean right) {
    return compareFalseFirst(left, right);
  }

  /**
   * Compares two {@code boolean} values, considering {@code true} to be less
   * than {@code false}, <i>if the result of this comparison chain has not
   * already been determined.
   *
   * @since 12.0
   */
  public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);

  /**
   * Compares two {@code boolean} values, considering {@code false} to be less
   * than {@code true}, <i>if the result of this comparison chain has not
   * already been determined.
   *
   * @since 12.0 (present as {@code compare} since 2.0)
   */
  public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);

  /**
   * Ends this comparison chain and returns its result: a value having the
   * same sign as the first nonzero comparison result in the chain, or zero if
   * every result was zero.
   */
  public abstract int result();
}
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