tokenstack.java

jboss规则引擎

package org.drools.leaps.util;

/*
 * Copyright 2005 JBoss Inc
 * 
 * Licensed 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.
 */

import java.io.Serializable;
import java.util.EmptyStackException;
import java.util.Iterator;

import org.drools.leaps.Token;
import org.drools.util.PrimitiveLongMap;

/**
 * This class follows java.util.Stack interface but accounts for remove( object )
 * functionallity needed by leaps
 * 
 * @author Alexander Bagerman
 * 
 */

public class TokenStack implements Serializable {

    protected TableRecord          tailRecord = null;

    private final PrimitiveLongMap map        = new PrimitiveLongMap( );

    public TokenStack() {

    }

    public boolean empty() {
        return this.tailRecord == null;
    }

    public Object peek() {
        if (this.tailRecord != null) {
            return this.tailRecord.object;
        }
        else {
            throw new EmptyStackException( );
        }
    }

    public Object pop() {
        if (this.tailRecord != null) {
            final Object ret = this.tailRecord.object;
            final TableRecord buf = this.tailRecord;
            this.tailRecord = buf.left;
            if (buf.left != null) {
                this.tailRecord.right = null;
            }
            buf.left = null;

            this.map.remove( ( (Token) ret ).getDominantFactHandle( ).getId( ) );
            return ret;
        }
        else {
            throw new EmptyStackException( );
        }
    }

    /**
     * Removes object from the table
     * 
     * @param object
     *            to remove from the table
     */
    public void remove( final long factId ) {
        if (this.tailRecord != null) {
            final TableRecord record = (TableRecord) this.map.remove( factId );

            if (record != null) {
                if (record == this.tailRecord) {
                    this.tailRecord = record.left;
                }
                if (record.left != null) {
                    record.left.right = record.right;
                }
                if (record.right != null) {
                    record.right.left = record.left;
                }
                record.left = null;
                record.right = null;
            }
        }
    }

    public Object push( final Object item ) {
        final TableRecord record = new TableRecord( item );
        if (this.tailRecord != null) {
            this.tailRecord.right = record;
            record.left = this.tailRecord;
        }
        this.tailRecord = record;

        this.map.put( ( (Token) item ).getDominantFactHandle( ).getId( ), record );
        return item;
    }

    public Iterator iterator() {
        return new Iterator( ) {
            Iterator it = TokenStack.this.map.values( ).iterator( );

            public boolean hasNext() {
                return this.it.hasNext( );
            }

            public void remove() {

            }

            public Object next() {
                return this.it.next( );
            }
        };
    }
}