001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    package org.apache.directory.shared.ldap.schema.comparators;
021    
022    
023    import java.io.Serializable;
024    import java.util.Comparator;
025    
026    
027    /**
028     * Compares two objects taking into account that one might be a Comparable.
029     * 
030     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
031     * @version $Rev: 736232 $
032     */
033    public class ComparableComparator implements Comparator, Serializable
034    {
035        private static final long serialVersionUID = -5295278271807198471L;
036    
037    
038        /**
039         * Compares two objects taking into account that one may be a Comparable. If
040         * the first is a comparable then its compareTo operation is called and the
041         * result returned as is. If the first is not a Comparable but the second is
042         * then its compareTo method is called and the result is returned after
043         * being negated. If none are comparables the hashCode of o1 minus the
044         * hashCode of o2 is returned.
045         * 
046         * @see Comparator#compare(Object, Object)
047         */
048        public int compare( Object o1, Object o2 )
049        {
050            if ( ( o1 == null ) && ( o2 == null ) )
051            {
052                return 0;
053            }
054            
055            if ( o1 instanceof Comparable )
056            {
057                if ( o2 == null )
058                {
059                    return -1;
060                }
061                else
062                {
063                    return ( ( Comparable ) o1 ).compareTo( o2 );
064                }
065            }
066    
067            if ( o2 == null )
068            {
069                return 1;
070            }
071            else if ( o2 instanceof Comparable )
072            {
073                if ( o1 == null )
074                {
075                    return -1;
076                }
077                else
078                {
079                    return -( ( Comparable ) o2 ).compareTo( o1 );
080                }
081            }
082    
083            // before https://issues.apache.org/jira/browse/DIRSERVER-928 it was
084            // return o1.hashCode() - o2.hashCode();
085            
086            // now we will blow a stack trace if none of the objects are Comparable
087            throw new IllegalArgumentException( "None of the arguments are Comparable objects:\n" 
088                + "\targ1 = " + o1 + "\n\targ2 = " + o2 );
089        }
090    }