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Posted to dev@commons.apache.org by js...@apache.org on 2002/06/11 18:22:06 UTC
cvs commit: jakarta-commons/collections/src/java/org/apache/commons/collections ComparatorUtils.java
jstrachan 2002/06/11 09:22:06
Added: collections/src/java/org/apache/commons/collections
ComparatorUtils.java
Log:
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.
Revision Changes Path
1.1 jakarta-commons/collections/src/java/org/apache/commons/collections/ComparatorUtils.java
Index: ComparatorUtils.java
===================================================================
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2001 The Apache Software Foundation. All rights
* reserved.
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* modification, are permitted provided that the following conditions
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*
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* distribution.
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* if any, must include the following acknowledgment:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgment may appear in the software itself,
* if and wherever such third-party acknowledgments normally appear.
*
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* derived from this software without prior written permission. For
* written permission, please contact apache@apache.org.
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* 5. Products derived from this software may not be called "Apache",
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package org.apache.commons.collections;
import java.util.Comparator;
import org.apache.commons.collections.comparators.ComparableComparator;
import org.apache.commons.collections.comparators.ReverseComparator;
import org.apache.commons.collections.comparators.NullComparator;
import org.apache.commons.collections.comparators.TransformingComparator;
/**
* Provides convenient static utility methods for <Code>Comparator</Code>
* objects.<P>
*
* Most of the utility in this class can also be found in the
* <Code>comparators</Code> package; this class merely provides a
* convenient central place if you have use for more than one class
* in the <Code>comparators</Code> subpackage.<P>
*
* Note that <I>every</I> method in this class allows you to specify
* <Code>null</Code> instead of a comparator, in which case
* {@link #NATURAL} will be used.
*
* @author Paul Jack
* @version $Id$
*/
public class ComparatorUtils {
/**
* Comparator for natural sort order.
*
* @see ComparableComparator#getInstance
*/
final public static Comparator NATURAL =
ComparableComparator.getInstance();
/**
* Returns a comparator that reverses the order of the given
* comparator.
*
* @param comparator the comparator whose order to reverse
* @return a comparator who reverses that order
* @see ReverseComparator
*/
public static Comparator reverse(Comparator comparator) {
if (comparator == null) comparator = NATURAL;
return new ReverseComparator(comparator);
}
/**
* Allows the given comparator to compare <Code>null</Code> values.<P>
*
* The returned comparator will consider a null value to be less than
* any nonnull value, and equal to any other null value. Two nonnull
* values will be evaluated with the given comparator.<P>
*
* @param comparator the comparator that wants to allow nulls
* @return a version of that comparator that allows nulls
* @see NullComparator
*/
public static Comparator nullFirst(Comparator comparator) {
if (comparator == null) comparator = NATURAL;
return new NullComparator(comparator, false);
}
/**
* Allows the given comparator to compare <Code>null</Code> values.<P>
*
* The returned comparator will consider a null value to be greater than
* any nonnull value, and equal to any other null value. Two nonnull
* values will be evaluated with the given comparator.<P>
*
* @param comparator the comparator that wants to allow nulls
* @return a version of that comparator that allows nulls
* @see NullComparator
*/
public static Comparator nullLast(Comparator comparator) {
if (comparator == null) comparator = NATURAL;
return new NullComparator(comparator, true);
}
/**
* Passes transformed objects to the given comparator.<P>
*
* Objects passed to the returned comparator will first be transformed
* by the given transformer before they are compared by the given
* comparator.<P>
*
* @param comparator the sort order to use
* @param t the transformer to use
* @return a comparator that transforms its input objects before
* comparing them
* @see TransformingComparator
*/
public static Comparator transform(Comparator comparator, Transformer t) {
if (comparator == null) comparator = NATURAL;
return new TransformingComparator(t, comparator);
}
/**
* Returns the smaller of the given objects according to the given
* comparator.
*
* @param o1 the first object to compare
* @param o2 the second object to compare
* @param comparator the sort order to use
* @return the smaller of the two objects
*/
public static Object min(Object o1, Object o2, Comparator comparator) {
if (comparator == null) comparator = NATURAL;
int c = comparator.compare(o1, o2);
return (c < 0) ? o1 : o2;
}
/**
* Returns the smaller of the given objects according to the given
* comparator.
*
* @param o1 the first object to compare
* @param o2 the second object to compare
* @param comparator the sort order to use
* @return the smaller of the two objects
*/
public static Object max(Object o1, Object o2, Comparator comparator) {
if (comparator == null) comparator = NATURAL;
int c = comparator.compare(o1, o2);
return (c > 0) ? o1 : o2;
}
}
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