emptymapiterator.java

jboss规则引擎

package org.drools.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.util.NoSuchElementException;

/**
 * Provides an implementation of an empty map iterator.
 * 
 * @since Commons Collections 3.1
 * @version $Revision: 1.1 $ $Date: 2005/07/26 01:06:32 $
 * 
 * @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(final Object obj) {
        throw new UnsupportedOperationException( "add() not supported for empty Iterator" );
    }

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

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