extendedcomparator.java

一个关于java 的常用工具包

package org.jutil.java.comparator;

import java.util.Comparator;

/**
 * <p>A Comparator with more convenient methods than <code>java.util.Comparator</code>.</p>
 *
 * @path    $Source: /cvsroot/org-jutil/jutil.org/src/org/jutil/java/comparator/ExtendedComparator.java,v $
 * @version $Revision: 1.4 $
 * @date    $Date: 2002/08/19 15:54:27 $
 * @state   $State: Exp $
 * @author  Tom Schrijvers
 * @author  Marko van Dooren
 * @release $Name:  $
 */
public abstract class ExtendedComparator implements Comparator {

  /* The revision of this class */
    public final static String CVS_REVISION ="$Revision: 1.4 $";

	/**
	 * <p>Return the maximum of both objects. In case of a tie, any
	 * one of both can be returned.</p>
	 *
	 * @param first
	 *        The first object
	 * @param second
	 *        The second object
	 */
 /*@
	 @ public behavior
	 @
	 @ post \result == first | \result == second;
	 @ post compare(\result, first) >= 0;
	 @ post compare(\result, second) >= 0;
	 @*/
	public Object max(Object first, Object second) {
		if (compare(first,second) >= 0) {
			return first;
		}
		return second;
	}
	
	/**
	 * <p>Return the minimum of both objects. In case of a tie, any
	 * one of both can be returned.</p>
	 *
	 * @param first
	 *        The first object
	 * @param second
	 *        The second object
	 */
 /*@
	 @ public behavior
	 @
	 @ post \result == first | \result == second;
	 @ post compare(\result, first) <= 0;
	 @ post compare(\result, second) <= 0;
	 @*/
	public Object min(Object first, Object second) {
		if (compare(first,second) <= 0) {
			return first;
		}
		return second;
	}

	/**
	 * <p>Check whether or not the first object is greater than
	 * the second one.</p>
	 *
	 * @param first
	 *        The first object
	 * @param second
	 *        The second object
	 */
 /*@
	 @ public behavior
	 @
	 @ post \result == (compare(first, second) > 0);
	 @*/
	public boolean greater(Object first, Object second) {
		return (compare(first,second) > 0);
	}

	/**
	 * <p>Check whether or not the first object is smaller than
	 * the second one.</p>
	 *
	 * @param first
	 *        The first object
	 * @param second
	 *        The second object
	 */
 /*@
	 @ public behavior
	 @
	 @ post \result == (compare(first, second) < 0);
	 @*/
	public boolean smaller(Object first, Object second) {
		return (compare(first,second) < 0);
	}


	/**
	 * <p>Check whether or not the first object is greater than
	 * or equal to the second one.</p>
	 *
	 * @param first
	 *        The first object
	 * @param second
	 *        The second object
	 */
 /*@
	 @ public behavior
	 @
	 @ post \result == ! smaller(first, second);
	 @*/
	public boolean notSmaller(Object first, Object second) {
		return (compare(first,second) >= 0);
	}

	/**
	 * <p>Check whether or not the first object is smaller than
	 * or equal to the second one.</p>
	 *
	 * @param first
	 *        The first object
	 * @param second
	 *        The second object
	 */
 /*@
	 @ public behavior
	 @
	 @ post \result == ! greater(first, second);
	 @*/
	public boolean notGreater(Object first, Object second) {
		return (compare(first,second) <= 0);
	}

	/**
	 * Ensure that the result is an ExtendedComparator.
	 * If the given Comparator is not an ExtendedComparator, it
	 * will be wrapped.
	 *
	 * @param comparator
	 *        The comparator of which one wants an ExtendedComparator
	 *        that behaves the same.
	 */
 /*@
	 @ public behavior
	 @
	 @ pre comparator != null;
	 @
	 @ // The result must behave exactly the same as the given comparator.
	 @ post (\forall Object o1; ;
	 @       (\forall Object o2; ;
	 @         \result.compare(o1, o2) == comparator.compare(o1, o2)));
	 @*/
	public static ExtendedComparator ensureExtended(Comparator comparator) {
		if (comparator instanceof ExtendedComparator) {
			return (ExtendedComparator) comparator;
		}
		else {
			return new ExtendedComparatorWrapper(comparator);
		}
	}

	/**
	 * An ExtendedComparator that wraps around a normal Comparator.
	 */
	private static class ExtendedComparatorWrapper extends ExtendedComparator {

		/**
		 * Initialize a new ExtendedComparator that wraps the given comparator.
		 *
		 * @param comparator
		 *        The Comparator to wrap.
		 */
	 /*@
		 @ public behavior
		 @
		 @ pre comparator != null;
		 @
		 @ post getComparator() == comparator;
		 @*/
		public ExtendedComparatorWrapper(Comparator comparator) {
			$comparator = comparator;
		}

		/**
		 * See superclass
		 */
	 /*@
		 @ also public behavior
		 @
		 @ post \result == getComparator().compare(first, second);
		 @*/
		public int compare(Object first, Object second) {
			return $comparator.compare(first, second);
		}

		/**
		 * Return the wrapped Comparator.
		 */
	 /*@
		 @ public behavior
		 @
		 @ post \result != null;
		 @*/
		public Comparator getComparator() {
			return $comparator;
		}

		/**
		 * The wrapped comparator.
		 */
	 /*@
		 @ private invariant $comparator != null;
		 @*/
		private final Comparator $comparator;
	}

}
/*
 * <copyright>Copyright (C) 1997-2001. This software is copyrighted by 
 * the people and entities mentioned after the "@author" tags above, on 
 * behalf of the JUTIL.ORG Project. The copyright is dated by the dates 
 * after the "@date" tags above. All rights reserved.
 * This software is published under the terms of the JUTIL.ORG Software
 * License version 1.1 or later, a copy of which has been included with
 * this distribution in the LICENSE file, which can also be found at
 * http://org-jutil.sourceforge.net/LICENSE. This software is distributed 
 * WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 
 * See the JUTIL.ORG Software License for more details. For more information,
 * please see http://org-jutil.sourceforge.net/</copyright>
 */