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From morg...@apache.org
Subject cvs commit: jakarta-commons/collections/src/java/org/apache/commons/collections/comparators ComparatorChain.java
Date Fri, 01 Mar 2002 23:29:24 GMT
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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