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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 com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/** An ordering that treats {@code null} as less than all other values. */
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
final class NullsFirstOrdering<T extends @Nullable Object> extends Ordering<@Nullable T>
implements Serializable {
final Ordering<? super T> ordering;
NullsFirstOrdering(Ordering<? super T> ordering) {
this.ordering = ordering;
}
@Override
public int compare(@CheckForNull T left, @CheckForNull T right) {
if (left == right) {
return 0;
}
if (left == null) {
return RIGHT_IS_GREATER;
}
if (right == null) {
return LEFT_IS_GREATER;
}
return ordering.compare(left, right);
}
@Override
@SuppressWarnings("nullness") // should be safe, but not sure if we can avoid the warning
public <S extends @Nullable T> Ordering<S> reverse() {
// ordering.reverse() might be optimized, so let it do its thing
return ordering.reverse().nullsLast();
}
@SuppressWarnings("unchecked") // still need the right way to explain this
@Override
public <S extends T> Ordering<@Nullable S> nullsFirst() {
return (Ordering<@Nullable S>) this;
}
@Override
public <S extends T> Ordering<@Nullable S> nullsLast() {
return ordering.<S>nullsLast();
}
@Override
public boolean equals(@CheckForNull Object object) {
if (object == this) {
return true;
}
if (object instanceof NullsFirstOrdering) {
NullsFirstOrdering<?> that = (NullsFirstOrdering<?>) object;
return this.ordering.equals(that.ordering);
}
return false;
}
@Override
public int hashCode() {
return ordering.hashCode() ^ 957692532; // meaningless
}
@Override
public String toString() {
return ordering + ".nullsFirst()";
}
private static final long serialVersionUID = 0;
}
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