facthandlelist.java

rule engine drools-2.0-beta-18

package org.drools.reteoo;

/*
* $Id: FactHandleList.java,v 1.2 2004/12/01 14:19:33 simon Exp $
*
* Copyright 2001-2004 (C) The Werken Company. All Rights Reserved.
*
* Redistribution and use of this software and associated documentation
* ("Software"), with or without modification, are permitted provided that the
* following conditions are met:
*
* 1. Redistributions of source code must retain copyright statements and
* notices. Redistributions must also contain a copy of this document.
*
* 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 name "drools" must not be used to endorse or promote products derived
* from this Software without prior written permission of The Werken Company.
* For written permission, please contact [e-mail].
*
* 4. Products derived from this Software may not be called "drools" nor may
* "drools" appear in their names without prior written permission of The Werken
* Company. "drools" is a trademark of The Werken Company.
*
* 5. Due credit should be given to The Werken Company. (http://werken.com/)
*
* THIS SOFTWARE IS PROVIDED BY THE WERKEN COMPANY AND CONTRIBUTORS ``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 WERKEN COMPANY 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.
*
*/

import org.drools.FactHandle;
import org.drools.rule.Declaration;

import java.io.Serializable;
import java.util.Arrays;

/**
 * Specialised array of {@link FactHandle}s intended to be keyed by a {@link Declaration}s
 * index. The list only ever contains as many elements as necessary to hold a handle at the
 * position specified by the largest Declaration index. As a result, the list will neccessarily
 * contain <code>NULL</code> values.
 *
 * This class exists purely for performance reasons and as such, many assumptions have been
 * made regarding behaviour based on know usage. Therefore, this class should in no way be
 * considerd a general purpose data structure. Hence it resides in this package and not a more
 * generic "util" package.
 *
 * @author <a href="mailto:[e-mail]">Simon Harris</a>
 */
final class FactHandleList implements Serializable
{
    /** Empty list for testing purposes only. */
    static final FactHandleList EMPTY_LIST = new FactHandleList( );

    /** The list of handles. */
    private final FactHandle[]  handles;

    /** The cached hash code value. */
    private final int           hashCode;

    /**
     * Private constructor for creating the {@link #EMPTY_LIST}.
     */
    private FactHandleList()
    {
        handles = new FactHandleImpl[ 0 ];
        hashCode = 0;
    }

    /**
     * Join two lists.
     * @param left The left list.
     * @param right The right list.
     */
    public FactHandleList( FactHandleList left,
                           FactHandleList right )
    {
        this.handles = new FactHandle[ Math.max( left.handles.length, right.handles.length ) ];

        System.arraycopy( left.handles, 0, this.handles, 0, left.handles.length );

        int hashCode = left.hashCode;
        FactHandle handle;

        for ( int i = right.handles.length - 1; i >= 0; i-- )
        {
            handle = right.handles[ i ];
            if ( handle != null && this.handles[ i ] == null )
            {
                this.handles[ i ] = handle;
                hashCode += handle.hashCode( );
            }
        }

        this.hashCode = hashCode;
    }

    /**
     * Single value constructor.
     * @param index The index at which the handle will be placed.
     * @param handle The handle to use.
     */
    public FactHandleList( int index, FactHandle handle )
    {
        this.handles = new FactHandleImpl[ index + 1 ];
        this.handles[ index ] = handle;
        this.hashCode = handle.hashCode( );
    }

    /**
     * Obtains the handle at a specified index.
     * @param index The position from which the handle should be obtained.
     * @return The handle; or <code>null</code> if no handle exists.
     * @throws ArrayIndexOutOfBoundsException if <code>index</code> &gt; {@link #length()}.
     */
    public FactHandle get( int index )
    {
        return this.handles[ index ];
    }

    /**
     * Determines if the list contains a specified handle.
     * @param handle The handle to search for.
     * @return <code>true</code> if the handle is found; otherwise <code>false</code>
     */
    public boolean contains( FactHandle handle )
    {
        for ( int i = handles.length - 1; i >= 0; i-- )
        {
            if ( handle.equals( handles[ i ] ) )
            {
                return true;
            }
        }

        return false;
    }

    /**
     * Determines if the list is a super-set of another list.
     * @param other The list to be checked.
     * @return <code>true</code> if this list contains all values from the other list; <code>false otherwise.
     */
    public boolean containsAll( FactHandleList other )
    {
        if ( other.handles.length > this.handles.length )
        {
            return false;
        }

        FactHandle handle;
        for ( int i = other.handles.length - 1; i >= 0; i-- )
        {
            handle = other.handles[ i ];
            if ( handle != null && !handle.equals( this.handles[ i ] ) )
            {
                return false;
            }
        }
        return true;
    }

    /**
     * Obtains the length of the list.
     * @return The length of the list, including all <code>null</code> values.
     */
    public int length()
    {
        return this.handles.length;
    }

    public int hashCode()
    {
        return this.hashCode;
    }

    public boolean equals( Object object )
    {
        if ( this == object )
        {
            return true;
        }

        if ( object instanceof FactHandleList )
        {
            return Arrays.equals( this.handles, ( ( FactHandleList ) object ).handles );
        }

        return false;
    }
}