class that allows you to chain comparators together for SQL-like

sorting...more Javadocs to come


git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/collections/trunk@130628 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/collections/comparators/ComparatorChain.java

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+/*
+ * $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/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;
+    }
+
+}