emptymapiterator.java

drools 一个开放源码的规则引擎

package org.drools.util;

import java.util.NoSuchElementException;

/*
 *  Copyright 2004 The Apache Software Foundation
 *
 *  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.
 */

/**
 * Provides an implementation of an empty map iterator.
 *
 * @since Commons Collections 3.1
 * @version $Revision: 1.4 $ $Date: 2004/12/06 01:30:38 $
 *
 * @author Stephen Colebourne
 */
public class EmptyMapIterator
    implements
    MapIterator
{

    /**
     * Singleton instance of the iterator.
     *
     * @since Commons Collections 3.1
     */
    public static final MapIterator INSTANCE = new EmptyMapIterator( );

    /**
     * Constructor.
     */
    protected EmptyMapIterator()
    {
    }

    public boolean hasNext()
    {
        return false;
    }

    public Object next()
    {
        throw new NoSuchElementException( "Iterator contains no elements" );
    }

    public boolean hasPrevious()
    {
        return false;
    }

    public Object previous()
    {
        throw new NoSuchElementException( "Iterator contains no elements" );
    }

    public int nextIndex()
    {
        return 0;
    }

    public int previousIndex()
    {
        return -1;
    }

    public void add( Object obj )
    {
        throw new UnsupportedOperationException( "add() not supported for empty Iterator" );
    }

    public void set( Object obj )
    {
        throw new IllegalStateException( "Iterator contains no elements" );
    }

    public void remove()
    {
        throw new IllegalStateException( "Iterator contains no elements" );
    }

    public Object getKey()
    {
        throw new IllegalStateException( "Iterator contains no elements" );
    }

    public Object getValue()
    {
        throw new IllegalStateException( "Iterator contains no elements" );
    }

    public Object setValue( Object value )
    {
        throw new IllegalStateException( "Iterator contains no elements" );
    }

    public void reset()
    {
        // do nothing
    }
}