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'rapiddweller Common' is an open source Java library forked from Databene Commons 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 com.rapiddweller.common;

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 {

  /**
   * The constant NULL_IS_LESSER.
   */
  public static final int NULL_IS_LESSER = -1;
  /**
   * The constant NULL_IS_GREATER.
   */
  public static final int NULL_IS_GREATER = 1;

  private final Comparator realComparator;

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

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

  /**
   * Instantiates a new Null safe comparator.
   */
  @SuppressWarnings({"unchecked", "rawtypes"})
  public NullSafeComparator() {
    this(new ComparableComparator());
  }

  /**
   * Instantiates a new Null safe comparator.
   *
   * @param nullComparation the null comparation
   */
  @SuppressWarnings({"unchecked", "rawtypes"})
  public NullSafeComparator(int nullComparation) {
    this(new ComparableComparator(), nullComparation);
  }

  /**
   * Instantiates a new Null safe comparator.
   *
   * @param realComparator the real comparator
   */
  public NullSafeComparator(Comparator realComparator) {
    this(realComparator, -1);
  }

  /**
   * Instantiates a new Null safe comparator.
   *
   * @param realComparator  the real comparator
   * @param nullComparation the null comparation
   */
  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);
    }
  }

  /**
   * Compare int.
   *
   * @param              the type parameter
   * @param o1              the o 1
   * @param o2              the o 2
   * @param nullComparation the null comparation
   * @return the int
   */
  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);
    }
  }

  /**
   * Equals boolean.
   *
   * @param o1 the o 1
   * @param o2 the o 2
   * @return the boolean
   */
  public static boolean equals(Object o1, Object o2) {
    if (o1 == null) {
      return (o2 == null);
    } else {
      return o1.equals(o2);
    }
  }

  /**
   * Hash code int.
   *
   * @param o the o
   * @return the int
   */
  public static int hashCode(Object o) {
    return (o != null ? o.hashCode() : 0);
  }
}