CompareNullSafe.java

/*******************************************************************************
 * Copyright 2013 André Rouél
 * 
 * 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 net.sf.uadetector.internal.util;

import java.io.Serializable;
import java.util.Comparator;

/**
 * Compares two references to each other and {@code null} is assumed to be less than a non-{@code null} value. This
 * class provides the first check for null safe comparison.
 * 
 * @author André Rouél
 */
public abstract class CompareNullSafe<T> implements Comparator<T>, Serializable {

    private static final long serialVersionUID = -704997500621650775L;

    /**
     * Compares to integers.
     * 
     * @param a
     *            first integer
     * @param b
     *            second integer
     * @return {@code -1} if {@code a} is less, {@code 0} if equal, or {@code 1} if greater than {@code b}
     */
    public static int compareInt(final int a, final int b) {
        return a > b ? 1 : a == b ? 0 : -1;
    }

    /**
     * Compares two objects null safe to each other.
     * 
     * @param o1
     *            the first reference
     * @param o2
     *            the second reference
     * @return a negative value if o1 < o2, zero if o1 = o2 and a positive value if o1 > o2
     */
    @Override
    public int compare(final T o1, final T o2) {
        int result = 0;
        if (o1 == null) {
            if (o2 != null) {
                result = -1;
            }
        } else if (o2 == null) {
            result = 1;
        } else {
            result = compareType(o1, o2);
        }
        return result;
    }

    public abstract int compareType(final T o1, final T o2);

}