applied Paul Jacks' patch for a number of helper methods for working with Comparators.
This can help avoid folks having to use the o.a*.c*.collections.comparators package, providing nice simple static helper method instead along the same lines as java.util.Collections and CollectionUtils here. git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/collections/trunk@130714 13f79535-47bb-0310-9956-ffa450edef68
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James Strachan
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/* ====================================================================
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* The Apache Software License, Version 1.1
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*
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* Copyright (c) 2001 The Apache Software Foundation. All rights
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* reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* 3. The end-user documentation included with the redistribution,
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* if any, must include the following acknowledgment:
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* "This product includes software developed by the
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* Apache Software Foundation (http://www.apache.org/)."
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* Alternately, this acknowledgment may appear in the software itself,
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* if and wherever such third-party acknowledgments normally appear.
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*
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* 4. The names "Apache" and "Apache Software Foundation" and
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* "Apache Commons" must not be used to endorse or promote products
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* derived from this software without prior written permission. For
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* written permission, please contact apache@apache.org.
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*
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* 5. Products derived from this software may not be called "Apache",
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* "Apache Turbine", nor may "Apache" appear in their name, without
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* prior written permission of the Apache Software Foundation.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
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* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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* ====================================================================
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*
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* This software consists of voluntary contributions made by many
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* individuals on behalf of the Apache Software Foundation. For more
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* information on the Apache Software Foundation, please see
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* <http://www.apache.org/>.
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*/
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package org.apache.commons.collections;
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import java.util.Comparator;
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import org.apache.commons.collections.comparators.ComparableComparator;
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import org.apache.commons.collections.comparators.ReverseComparator;
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import org.apache.commons.collections.comparators.NullComparator;
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import org.apache.commons.collections.comparators.TransformingComparator;
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/**
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* Provides convenient static utility methods for <Code>Comparator</Code>
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* objects.<P>
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*
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* Most of the utility in this class can also be found in the
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* <Code>comparators</Code> package; this class merely provides a
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* convenient central place if you have use for more than one class
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* in the <Code>comparators</Code> subpackage.<P>
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*
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* Note that <I>every</I> method in this class allows you to specify
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* <Code>null</Code> instead of a comparator, in which case
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* {@link #NATURAL} will be used.
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*
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* @author Paul Jack
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* @version $Id$
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*/
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public class ComparatorUtils {
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/**
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* Comparator for natural sort order.
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*
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* @see ComparableComparator#getInstance
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*/
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final public static Comparator NATURAL =
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ComparableComparator.getInstance();
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/**
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* Returns a comparator that reverses the order of the given
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* comparator.
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*
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* @param comparator the comparator whose order to reverse
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* @return a comparator who reverses that order
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* @see ReverseComparator
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*/
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public static Comparator reverse(Comparator comparator) {
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if (comparator == null) comparator = NATURAL;
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return new ReverseComparator(comparator);
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}
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/**
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* Allows the given comparator to compare <Code>null</Code> values.<P>
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*
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* The returned comparator will consider a null value to be less than
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* any nonnull value, and equal to any other null value. Two nonnull
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* values will be evaluated with the given comparator.<P>
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*
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* @param comparator the comparator that wants to allow nulls
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* @return a version of that comparator that allows nulls
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* @see NullComparator
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*/
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public static Comparator nullFirst(Comparator comparator) {
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if (comparator == null) comparator = NATURAL;
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return new NullComparator(comparator, false);
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}
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/**
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* Allows the given comparator to compare <Code>null</Code> values.<P>
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*
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* The returned comparator will consider a null value to be greater than
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* any nonnull value, and equal to any other null value. Two nonnull
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* values will be evaluated with the given comparator.<P>
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*
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* @param comparator the comparator that wants to allow nulls
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* @return a version of that comparator that allows nulls
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* @see NullComparator
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*/
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public static Comparator nullLast(Comparator comparator) {
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if (comparator == null) comparator = NATURAL;
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return new NullComparator(comparator, true);
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}
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/**
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* Passes transformed objects to the given comparator.<P>
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*
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* Objects passed to the returned comparator will first be transformed
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* by the given transformer before they are compared by the given
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* comparator.<P>
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*
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* @param comparator the sort order to use
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* @param t the transformer to use
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* @return a comparator that transforms its input objects before
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* comparing them
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* @see TransformingComparator
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*/
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public static Comparator transform(Comparator comparator, Transformer t) {
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if (comparator == null) comparator = NATURAL;
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return new TransformingComparator(t, comparator);
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}
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/**
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* Returns the smaller of the given objects according to the given
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* comparator.
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*
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* @param o1 the first object to compare
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* @param o2 the second object to compare
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* @param comparator the sort order to use
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* @return the smaller of the two objects
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*/
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public static Object min(Object o1, Object o2, Comparator comparator) {
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if (comparator == null) comparator = NATURAL;
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int c = comparator.compare(o1, o2);
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return (c < 0) ? o1 : o2;
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}
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/**
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* Returns the smaller of the given objects according to the given
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* comparator.
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*
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* @param o1 the first object to compare
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* @param o2 the second object to compare
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* @param comparator the sort order to use
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* @return the smaller of the two objects
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*/
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public static Object max(Object o1, Object o2, Comparator comparator) {
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if (comparator == null) comparator = NATURAL;
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int c = comparator.compare(o1, o2);
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return (c > 0) ? o1 : o2;
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}
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}
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