Commons Collections example source code file (ComparatorChain.java)

This example Commons Collections source code file (ComparatorChain.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Collections tags/keywords

arraylist, bitset, bitset, comparator, comparator, comparatorchain, comparatorchain, comparatorchains, indexoutofboundsexception, io, iterator, object, serializable, unsupportedoperationexception, unsupportedoperationexception, util

The Commons Collections ComparatorChain.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
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.  However, <i>take care
 * to not alter the underlying List of Comparators
 * or the BitSet that defines the sort order.</p>
 * 
 * <p>Instances of ComparatorChain are not synchronized.
 * The class is not thread-safe at construction time, but
 * it <i>is thread-safe to perform multiple comparisons
 * after all the setup operations are complete.</p>
 * 
 * @since Commons Collections 2.0
 * @author Morgan Delagrange
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 */
public class ComparatorChain implements Comparator, Serializable {

    /** Serialization version from Collections 2.0. */
    private static final long serialVersionUID = -721644942746081630L;
    
    /** The list of comparators in the chain. */
    protected List comparatorChain = null;
    /** Order - false (clear) = ascend; true (set) = descend. */
    protected BitSet orderingBits = null;
   /** Whether the chain has been "locked". */
    protected boolean isLocked = false;

    //-----------------------------------------------------------------------
    /**
     * Construct a ComparatorChain with no Comparators.
     * You must add at least one Comparator before calling
     * the compare(Object,Object) method, or an 
     * UnsupportedOperationException is thrown
     */
    public ComparatorChain() {
        this(new ArrayList(),new BitSet());
    }

    /**
     * Construct a ComparatorChain with a single Comparator,
     * sorting in the forward order
     * 
     * @param comparator First comparator in the Comparator chain
     */
    public ComparatorChain(Comparator comparator) {
        this(comparator,false);
    }

    /**
     * Construct a Comparator chain with a single Comparator,
     * sorting in the given order
     * 
     * @param comparator First Comparator in the ComparatorChain
     * @param reverse    false = forward sort; true = reverse sort
     */
    public ComparatorChain(Comparator comparator, boolean reverse) {
        comparatorChain = new ArrayList();
        comparatorChain.add(comparator);
        orderingBits = new BitSet(1);
        if (reverse == true) {
            orderingBits.set(0);
        }
    }

    /**
     * Construct a ComparatorChain from the Comparators in the
     * List.  All Comparators will default to the forward 
     * sort order.
     * 
     * @param list   List of Comparators
     * @see #ComparatorChain(List,BitSet)
     */
    public ComparatorChain(List list) {
        this(list,new BitSet(list.size()));
    }

    /**
     * Construct a ComparatorChain from the Comparators in the
     * given List.  The sort order of each column will be
     * drawn from the given BitSet.  When determining the sort
     * order for Comparator at index <i>i in the List,
     * the ComparatorChain will call BitSet.get(<i>i).
     * If that method returns <i>false, the forward
     * sort order is used; a return value of <i>true
     * indicates reverse sort order.
     * 
     * @param list   List of Comparators.  NOTE: This constructor does not perform a
     *               defensive copy of the list
     * @param bits   Sort order for each Comparator.  Extra bits are ignored,
     *               unless extra Comparators are added by another method.
     */
    public ComparatorChain(List list, BitSet bits) {
        comparatorChain = list;
        orderingBits = bits;
    }

    //-----------------------------------------------------------------------
    /**
     * Add a Comparator to the end of the chain using the
     * forward sort order
     * 
     * @param comparator Comparator with the forward sort order
     */
    public void addComparator(Comparator comparator) {
        addComparator(comparator,false);
    }

    /**
     * Add a Comparator to the end of the chain using the
     * given sort order
     * 
     * @param comparator Comparator to add to the end of the chain
     * @param reverse    false = forward sort order; true = reverse sort order
     */
    public void addComparator(Comparator comparator, boolean reverse) {
        checkLocked();
        
        comparatorChain.add(comparator);
        if (reverse == true) {
            orderingBits.set(comparatorChain.size() - 1);
        }
    }

    /**
     * Replace the Comparator at the given index, maintaining
     * the existing sort order.
     * 
     * @param index      index of the Comparator to replace
     * @param comparator Comparator to place at the given index
     * @exception IndexOutOfBoundsException
     *                   if index < 0 or index >= size()
     */
    public void setComparator(int index, Comparator comparator) 
    throws IndexOutOfBoundsException {
        setComparator(index,comparator,false);
    }

    /**
     * Replace the Comparator at the given index in the
     * ComparatorChain, using the given sort order
     * 
     * @param index      index of the Comparator to replace
     * @param comparator Comparator to set
     * @param reverse    false = forward sort order; true = reverse sort order
     */
    public void setComparator(int index, Comparator comparator, boolean reverse) {
        checkLocked();

        comparatorChain.set(index,comparator);
        if (reverse == true) {
            orderingBits.set(index);
        } else {
            orderingBits.clear(index);
        }
    }


    /**
     * Change the sort order at the given index in the
     * ComparatorChain to a forward sort.
     * 
     * @param index  Index of the ComparatorChain
     */
    public void setForwardSort(int index) {
        checkLocked();
        orderingBits.clear(index);
    }

    /**
     * Change the sort order at the given index in the
     * ComparatorChain to a reverse sort.
     * 
     * @param index  Index of the ComparatorChain
     */
    public void setReverseSort(int index) {
        checkLocked();
        orderingBits.set(index);
    }

    /**
     * Number of Comparators in the current ComparatorChain.
     * 
     * @return Comparator count
     */
    public int size() {
        return comparatorChain.size();
    }

    /**
     * Determine if modifications can still be made to the
     * ComparatorChain.  ComparatorChains cannot be modified
     * once they have performed a comparison.
     * 
     * @return true = ComparatorChain cannot be modified; false = 
     *         ComparatorChain can still be modified.
     */
    public boolean isLocked() {
        return isLocked;
    }

    // throw an exception if the ComparatorChain is locked
    private void checkLocked() {
        if (isLocked == true) {
            throw new UnsupportedOperationException("Comparator ordering cannot be changed after the first comparison is performed");
        }
    }

    private void checkChainIntegrity() {
        if (comparatorChain.size() == 0) {
            throw new UnsupportedOperationException("ComparatorChains must contain at least one Comparator");
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Perform comparisons on the Objects as per
     * Comparator.compare(o1,o2).
     * 
     * @param o1  the first object to compare
     * @param o2  the second object to compare
     * @return -1, 0, or 1
     * @exception UnsupportedOperationException
     *                   if the ComparatorChain does not contain at least one
     *                   Comparator
     */
    public int compare(Object o1, Object o2) throws UnsupportedOperationException {
        if (isLocked == false) {
            checkChainIntegrity();
            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) {
                    if(Integer.MIN_VALUE == retval) {
                        retval = Integer.MAX_VALUE;
                    } else {                        
                        retval *= -1;
                    }
                }

                return retval;
            }

        }

        // if comparators are exhausted, return 0
        return 0;
    }

    //-----------------------------------------------------------------------
    /**
     * Implement a hash code for this comparator that is consistent with
     * {@link #equals(Object) equals}.
     * 
     * @return a suitable hash code
     * @since Commons Collections 3.0
     */
    public int hashCode() {
        int hash = 0;
        if(null != comparatorChain) {
            hash ^= comparatorChain.hashCode();
        }
        if(null != orderingBits) {
            hash ^= orderingBits.hashCode();
        }
        return hash;
    }

    /**
     * Returns <code>true iff that Object is 
     * is a {@link Comparator} whose ordering is known to be 
     * equivalent to mine.
     * <p>
     * This implementation returns <code>true
     * iff <code>object.{@link Object#getClass() getClass()}
     * equals <code>this.getClass(), and the underlying 
     * comparators and order bits are equal.
     * Subclasses may want to override this behavior to remain consistent
     * with the {@link Comparator#equals(Object)} contract.
     * 
     * @param object  the object to compare with
     * @return true if equal
     * @since Commons Collections 3.0
     */
    public boolean equals(Object object) {
        if(this == object) {
            return true;
        } else if(null == object) {
            return false;
        } else if(object.getClass().equals(this.getClass())) {
            ComparatorChain chain = (ComparatorChain)object;
            return ( (null == orderingBits ? null == chain.orderingBits : orderingBits.equals(chain.orderingBits))
                   && (null == comparatorChain ? null == chain.comparatorChain : comparatorChain.equals(chain.comparatorChain)) );
        } else {
            return false;
        }
    }

}