All Downloads are FREE. Search and download functionalities are using the official Maven repository.

com.google.common.collect.ComparisonChain Maven / Gradle / Ivy

Go to download

This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

The newest version!
/*
 * 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 org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A utility for performing a chained comparison statement. Note: Java 8+ users should
 * generally prefer the methods in {@link Comparator}; see below.
 *
 * 
Example usage of {@code ComparisonChain}:
 *
 * 
{@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();
 * }
 * }

 *
 * 
The value of this expression will have the same sign as the first nonzero comparison
 * result in the chain, or will be zero if every comparison result was zero.
 *
 * 
Note: {@code ComparisonChain} instances are immutable. For this utility to work
 * correctly, calls must be chained as illustrated above.
 *
 * 
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.
 *
 * 
See the Guava User Guide article on {@code
 * ComparisonChain}.
 *
 * 
Java 8+ equivalents

 *
 * If you are using Java version 8 or greater, you should generally use the static methods in {@link
 * Comparator} instead of {@code ComparisonChain}. The example above can be implemented like this:
 *
 * 
{@code
 * import static java.util.Comparator.comparing;
 * import static java.util.Comparator.nullsLast;
 * import static java.util.Comparator.naturalOrder;
 *
 * ...
 *   private static final Comparator COMPARATOR =
 *       comparing((Foo foo) -> foo.aString)
 *           .thenComparing(foo -> foo.anInt)
 *           .thenComparing(foo -> foo.anEnum, nullsLast(naturalOrder()));}
 *
 *   {@code @Override}{@code
 *   public int compareTo(Foo that) {
 *     return COMPARATOR.compare(this, that);
 *   }
 * }

 *
 * 
With method references it is more succinct: {@code comparing(Foo::aString)} for example.
 *
 * 
Using {@link Comparator} avoids certain types of bugs, for example when you meant to write
 * {@code .compare(a.foo, b.foo)} but you actually wrote {@code .compare(a.foo, a.foo)} or {@code
 * .compare(a.foo, b.bar)}. {@code ComparisonChain} also has a potential performance problem that
 * {@code Comparator} doesn't: it evaluates all the parameters of all the {@code .compare} calls,
 * even when the result of the comparison is already known from previous {@code .compare} calls.
 * That can be expensive.
 *
 * @author Mark Davis
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ComparisonChain {
  private ComparisonChain() {}

  /** Begins a new chained comparison statement. See example in the class documentation. */
  public static ComparisonChain start() {
    return ACTIVE;
  }

  private static final ComparisonChain ACTIVE =
      new ComparisonChain() {
        @SuppressWarnings("unchecked") // unsafe; see discussion on supertype
        @Override
        public ComparisonChain compare(Comparable left, Comparable right) {
          return classify(((Comparable) left).compareTo(right));
        }

        @Override
        public  ComparisonChain compare(
            @ParametricNullness T left, @ParametricNullness T right, Comparator comparator) {
          return classify(comparator.compare(left, right));
        }

        @Override
        public ComparisonChain compare(int left, int right) {
          return classify(Ints.compare(left, right));
        }

        @Override
        public ComparisonChain compare(long left, long right) {
          return classify(Longs.compare(left, right));
        }

        @Override
        public ComparisonChain compare(float left, float right) {
          return classify(Float.compare(left, right));
        }

        @Override
        public ComparisonChain compare(double left, double right) {
          return classify(Double.compare(left, right));
        }

        @Override
        public ComparisonChain compareTrueFirst(boolean left, boolean right) {
          return classify(Booleans.compare(right, left)); // reversed
        }

        @Override
        public ComparisonChain compareFalseFirst(boolean left, boolean right) {
          return classify(Booleans.compare(left, right));
        }

        ComparisonChain classify(int result) {
          return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
        }

        @Override
        public int result() {
          return 0;
        }
      };

  private static final ComparisonChain LESS = new InactiveComparisonChain(-1);

  private static final ComparisonChain GREATER = new InactiveComparisonChain(1);

  private static final class InactiveComparisonChain extends ComparisonChain {
    final int result;

    InactiveComparisonChain(int result) {
      this.result = result;
    }

    @Override
    public ComparisonChain compare(Comparable left, Comparable right) {
      return this;
    }

    @Override
    public  ComparisonChain compare(
        @ParametricNullness T left, @ParametricNullness T right, Comparator comparator) {
      return this;
    }

    @Override
    public ComparisonChain compare(int left, int right) {
      return this;
    }

    @Override
    public ComparisonChain compare(long left, long right) {
      return this;
    }

    @Override
    public ComparisonChain compare(float left, float right) {
      return this;
    }

    @Override
    public ComparisonChain compare(double left, double right) {
      return this;
    }

    @Override
    public ComparisonChain compareTrueFirst(boolean left, boolean right) {
      return this;
    }

    @Override
    public ComparisonChain compareFalseFirst(boolean left, boolean right) {
      return this;
    }

    @Override
    public int result() {
      return result;
    }
  }

  /**
   * Compares two comparable objects as specified by {@link Comparable#compareTo}, if the
   * result of this comparison chain has not already been determined.
   *
   * 
This method is declared to accept any 2 {@code Comparable} objects, even if they are not mutually
   * comparable. If you pass objects that are not mutually comparable, this method may throw an
   * exception. (The reason for this decision is lost to time, but the reason might be that
   * we wanted to support legacy classes that implement the raw type {@code Comparable} (instead of
   * implementing {@code Comparable}) without producing warnings. If so, we would prefer today
   * to produce warnings in that case, and we may change this method to do so in the future. Support
   * for raw {@code Comparable} types in Guava in general is tracked as #989.)
   *
   * @throws ClassCastException if the parameters are not mutually comparable
   */
  public abstract ComparisonChain compare(Comparable left, Comparable right);

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

  /**
   * Compares two {@code int} values as specified by {@link Ints#compare}, 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}, 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}, 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}, 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},
   * if the result of this comparison chain has not already been determined.
   *
   * 
Java 8+ users: you can get the equivalent from {@link Booleans#trueFirst()}. For example:
   *
   * 
   * Comparator.comparing(Foo::isBar, {@link Booleans#trueFirst()})
   * 

   *
   * @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},
   * if the result of this comparison chain has not already been determined.
   *
   * 
Java 8+ users: you can get the equivalent from {@link Booleans#falseFirst()}. For example:
   *
   * 
   * Comparator.comparing(Foo::isBar, {@link Booleans#falseFirst()})
   * 

   *
   * @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();
}
    

    

    

            

    

            



    
    






    
© 2015 - 2024 Weber Informatics LLC | Privacy Policy