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/*
* 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 javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/** An ordering that uses the natural order of the values. */
@GwtCompatible(serializable = true)
@SuppressWarnings({"unchecked", "rawtypes"}) // TODO(kevinb): the right way to explain this??
@ElementTypesAreNonnullByDefault
final class NaturalOrdering extends Ordering<Comparable<?>> implements Serializable {
static final NaturalOrdering INSTANCE = new NaturalOrdering();
@CheckForNull private transient Ordering<@Nullable Comparable<?>> nullsFirst;
@CheckForNull private transient Ordering<@Nullable Comparable<?>> nullsLast;
@Override
public int compare(Comparable<?> left, Comparable<?> right) {
checkNotNull(left); // for GWT
checkNotNull(right);
return ((Comparable<Object>) left).compareTo(right);
}
@Override
public <S extends Comparable<?>> Ordering<@Nullable S> nullsFirst() {
Ordering<@Nullable Comparable<?>> result = nullsFirst;
if (result == null) {
result = nullsFirst = super.<Comparable<?>>nullsFirst();
}
return (Ordering<@Nullable S>) result;
}
@Override
public <S extends Comparable<?>> Ordering<@Nullable S> nullsLast() {
Ordering<@Nullable Comparable<?>> result = nullsLast;
if (result == null) {
result = nullsLast = super.<Comparable<?>>nullsLast();
}
return (Ordering<@Nullable 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;
}
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