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Java example source code file (NaturalOrdering.java)

This example Java source code file (NaturalOrdering.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

comparable, gwtcompatible, instance, naturalordering, object, ordering, override, serializable, string, suppresswarnings, todo

The NaturalOrdering.java Java example source code

/*
 * Copyright (C) 2007 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 static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;

/** An ordering that uses the natural order of the values. */
@GwtCompatible(serializable = true)
@SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
final class NaturalOrdering extends Ordering<Comparable> implements Serializable {
  static final NaturalOrdering INSTANCE = new NaturalOrdering();

  private transient Ordering<Comparable> nullsFirst;
  private transient Ordering<Comparable> nullsLast;

  @Override
  public int compare(Comparable left, Comparable right) {
    checkNotNull(left); // for GWT
    checkNotNull(right);
    return left.compareTo(right);
  }

  @Override
  public <S extends Comparable> Ordering nullsFirst() {
    Ordering<Comparable> result = nullsFirst;
    if (result == null) {
      result = nullsFirst = super.nullsFirst();
    }
    return (Ordering<S>) result;
  }

  @Override
  public <S extends Comparable> Ordering nullsLast() {
    Ordering<Comparable> result = nullsLast;
    if (result == null) {
      result = nullsLast = super.nullsLast();
    }
    return (Ordering<S>) result;
  }

  @Override
  public <S extends Comparable> Ordering reverse() {
    return (Ordering<S>) ReverseNaturalOrdering.INSTANCE;
  }

  // preserving singleton-ness gives equals()/hashCode() for free
  private Object readResolve() {
    return INSTANCE;
  }

  @Override
  public String toString() {
    return "Ordering.natural()";
  }

  private NaturalOrdering() {}

  private static final long serialVersionUID = 0;
}

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