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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2010-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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.amazonaws.metrics.internal.cloudwatch;

import java.util.Comparator;

import com.amazonaws.services.cloudwatch.model.Dimension;

/**
 * Used to compare {@link Dimension}.
 *
 */
enum DimensionComparator implements Comparator {
    INSTANCE
    ;
    /** Used to indicate the two objects being compared are both non-nulls. */
    private static final int NON_NULLS = 2;

    @Override
    public int compare(Dimension dim1, Dimension dim2) {
        int result = nullCompare(dim1, dim2);
        if (result == NON_NULLS) {
            result = nullSafeCompare(dim1.getName(), dim2.getName());
            if (result == 0) {
                return nullSafeCompare(dim1.getValue(), dim2.getValue());
            }
        }
        return result;
    }

    /**
     * Compares the two given strings for order, handling null as necessary.
     * 
     * @return a negative integer, zero, or a positive integer as the first
     *         object is less than, equal to, or greater than the second object.
     */
    private int nullSafeCompare(String first, String second) {
        int result = nullCompare(first, second);
        return result == NON_NULLS ? first.compareTo(second) : result;
    }

    /**
     * Partially compares the two given objects for order, handling null as
     * necessary.
     * 
     * @return a -1 if the first object is null but not the second, 0 if both
     *         objects are identical, 1 if the second object is null but not the
     *         first. Otherwise, {@link #NON_NULLS} is returned which means both
     *         objects are non-null but not identical.
     */
    private int nullCompare(Object first, Object second) {
        if (first == second) {
            return 0;
        }
        if (first == null) {
            return -1;
        }
        if (second == null) {
            return 1;
        }
        return NON_NULLS;
    }
}