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'databene commons' is an open source Java library by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * 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.
 * 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.databene.commons;

import java.util.Comparator;

/**
 * Comparator Decorator that adds support for null-Value comparison.
 * null may be defined to have a value either greater or less than any non-null value.
 * Created: 11.04.2005 08:34:02
 * @param  the type of the objects to compare
 * @author Volker Bergmann
 */
public class NullSafeComparator implements Comparator {

    public static final int NULL_IS_LESSER   = -1;
    public static final int NULL_IS_GREATER =  1;

    private Comparator realComparator;

    /** The value returned if null is compared to something.
     */
    private int nullComparation;

    // constructors ----------------------------------------------------------------------------------------------------

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public NullSafeComparator() {
        this(new ComparableComparator());
    }

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public NullSafeComparator(int nullComparation) {
        this(new ComparableComparator(), nullComparation);
    }

    public NullSafeComparator(Comparator realComparator) {
        this(realComparator, -1);
    }

    public NullSafeComparator(Comparator realComparator, int nullComparation) {
        this.realComparator = realComparator;
        this.nullComparation = nullComparation;
    }

    // interface -------------------------------------------------------------------------------------------------------

    @Override
	public int compare(E o1, E o2) {
        if (o1 == o2)
            return 0;
        if (o1 == null)
            return (o2 == null ? 0 : nullComparation);
        else if (o2 == null)
            return -nullComparation;
        else
            return realComparator.compare(o1, o2);
    }

    public static > int compare(T o1, T o2, int nullComparation) {
        if (o1 == o2)
            return 0;
        if (o1 == null)
            return (o2 == null ? 0 : nullComparation);
        else if (o2 == null)
            return -nullComparation;
        else
            return o1.compareTo(o2);
    }

    public static boolean equals(Object o1, Object o2) {
        if (o1 == null)
            return (o2 == null);
        else
            return o1.equals(o2);
    }

	public static int hashCode(Object o) {
		return (o != null ? o.hashCode() : 0);
	}
}