/*
 * 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;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;

An ordering that uses the natural order of the values.
/** 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 @MonotonicNonNull Ordering<Comparable> nullsFirst; private transient @MonotonicNonNull 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<S> nullsFirst() { Ordering<Comparable> result = nullsFirst; if (result == null) { result = nullsFirst = super.nullsFirst(); } return (Ordering<S>) result; } @Override public <S extends Comparable> Ordering<S> nullsLast() { Ordering<Comparable> result = nullsLast; if (result == null) { result = nullsLast = super.nullsLast(); } return (Ordering<S>) result; } @Override public <S extends Comparable> Ordering<S> 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; }