NullsFirstOrdering.java

/*
 * 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 org.glassfish.jersey.internal.guava;

import java.io.Serializable;

/**
 * An ordering that treats {@code null} as less than all other values.
 */
final class NullsFirstOrdering<T> extends Ordering<T> implements Serializable {
    private static final long serialVersionUID = 0;
    private final Ordering<? super T> ordering;

    NullsFirstOrdering(Ordering<? super T> ordering) {
        this.ordering = ordering;
    }

    @Override
    public int compare(T left, 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
    public <S extends 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<S> nullsFirst() {
        return (Ordering<S>) this;
    }

    @Override
    public <S extends T> Ordering<S> nullsLast() {
        return ordering.nullsLast();
    }

    @Override
    public boolean equals(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()";
    }
}