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Posted to dev@commons.apache.org by mo...@apache.org on 2002/03/02 00:29:24 UTC
cvs commit: jakarta-commons/collections/src/java/org/apache/commons/collections/comparators ComparatorChain.java
morgand 02/03/01 15:29:24
Added: collections/src/java/org/apache/commons/collections/comparators
ComparatorChain.java
Log:
class that allows you to chain comparators together for SQL-like
sorting...more Javadocs to come
Revision Changes Path
1.1 jakarta-commons/collections/src/java/org/apache/commons/collections/comparators/ComparatorChain.java
Index: ComparatorChain.java
===================================================================
/*
* $Header: /home/cvs/jakarta-commons/collections/src/java/org/apache/commons/collections/comparators/ComparatorChain.java,v 1.1 2002/03/01 23:29:24 morgand Exp $
* $Revision: 1.1 $
* $Date: 2002/03/01 23:29:24 $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 1999-2001 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Group.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.commons.collections.comparators;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
/**
* <p>A ComparatorChain is a Comparator that wraps one or
* more Comparators in sequence. The ComparatorChain
* calls each Comparator in sequence until either 1)
* any single Comparator returns a non-zero result
* (and that result is then returned),
* or 2) the ComparatorChain is exhausted (and zero is
* returned). This type of sorting is very similar
* to multi-column sorting in SQL, and this class
* allows Java classes to emulate that kind of behaviour
* when sorting a List.</p>
*
* <p>To further facilitate SQL-like sorting, the order of
* any single Comparator in the list can be reversed.</p>
*
* <p>Calling a method that adds new Comparators or
* changes the ascend/descend sort <i>after compare(Object,
* Object) has been called</i> will result in an
* UnsupportedOperationException.</p>
*
* <p>Instances of ComparatorChain are not synchronized.</p>
*
* @author Morgan Delagrange
*/
public class ComparatorChain implements Comparator,Serializable {
protected List comparatorChain = null;
// 0 = ascend; 1 = descend
protected BitSet orderingBits = null;
// ComparatorChain is "locked" after the first time
// compare(Object,Object) is called)
protected boolean isLocked = false;
public ComparatorChain(Comparator comparator) {
this(comparator,false);
}
public ComparatorChain(Comparator comparator, boolean reverse) {
comparatorChain = new ArrayList();
comparatorChain.add(comparator);
orderingBits = new BitSet(1);
if (reverse == true) {
orderingBits.set(0);
}
}
/**
*
* @param list
* @see #ComparatorChain(List,BitSet)
*/
public ComparatorChain(List list) {
this(list,new BitSet(list.size()));
}
/**
*
* @param list WARNING: If this list is not modifiable, some
* subsequent modifications
* to the ComparatorChain can fail. Also, if you intend
* to serialize
* this ComparatorChain, then this List must also
* be Serializable.
* @param bits
*/
public ComparatorChain(List list, BitSet bits) {
comparatorChain = list;
orderingBits = bits;
}
public void addComparator(Comparator comparator) {
addComparator(comparator,false);
}
public void addComparator(Comparator comparator, boolean reverse) {
checkLocked();
comparatorChain.add(comparator);
if (reverse == true) {
orderingBits.set(comparatorChain.size() - 1);
}
}
public void setComparator(int index, Comparator comparator) {
setComparator(index,comparator,false);
}
public void setComparator(int index, Comparator comparator, boolean reverse) {
checkLocked();
comparatorChain.set(index,comparator);
if (reverse == true) {
orderingBits.set(index);
} else {
orderingBits.clear(index);
}
}
public void checkLocked() {
if (isLocked == true) {
throw new UnsupportedOperationException("Comparator ordering cannot be changed after the first comparison is performed");
}
}
public int compare(Object o1, Object o2) {
if (isLocked == false) {
isLocked = true;
}
// iterate over all comparators in the chain
Iterator comparators = comparatorChain.iterator();
for (int comparatorIndex = 0; comparators.hasNext(); ++comparatorIndex) {
Comparator comparator = (Comparator) comparators.next();
int retval = comparator.compare(o1,o2);
if (retval != 0) {
// invert the order if it is a reverse sort
if (orderingBits.get(comparatorIndex) == true) {
retval *= -1;
}
return retval;
}
}
// if comparators are exhausted, return 0
return 0;
}
}
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