mapiterator.java

rule engine drools-2.0-beta-18

package org.drools.util;
/*
 *  Copyright 2003-2004 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.
 */

import java.util.Iterator;

/**
 * Defines an iterator that operates over a <code>Map</code>.
 * <p>
 * This iterator is a special version designed for maps. It can be more
 * efficient to use this rather than an entry set iterator where the option is
 * available, and it is certainly more convenient.
 * <p>
 * A map that provides this interface may not hold the data internally using Map
 * Entry objects, thus this interface can avoid lots of object creation.
 * <p>
 * In use, this iterator iterates through the keys in the map. After each call
 * to <code>next()</code>, the <code>getValue()</code> method provides
 * direct access to the value. The value can also be set using
 * <code>setValue()</code>.
 * 
 * <pre>
 * MapIterator it = map.mapIterator( );
 * while ( it.hasNext( ) )
 * {
 *     Object key = it.next( );
 *     Object value = it.getValue( );
 *     it.setValue( newValue );
 * }
 * </pre>
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 1.2 $ $Date: 2004/11/19 02:15:18 $
 * 
 * @author Stephen Colebourne
 */
public interface MapIterator
    extends
    Iterator
{

    /**
     * Checks to see if there are more entries still to be iterated.
     * 
     * @return <code>true</code> if the iterator has more elements
     */
    boolean hasNext();

    /**
     * Gets the next <em>key</em> from the <code>Map</code>.
     * 
     * @return the next key in the iteration
     * @throws java.util.NoSuchElementException
     *             if the iteration is finished
     */
    Object next();

    // -----------------------------------------------------------------------
    /**
     * Gets the current key, which is the key returned by the last call to
     * <code>next()</code>.
     * 
     * @return the current key
     * @throws IllegalStateException
     *             if <code>next()</code> has not yet been called
     */
    Object getKey();

    /**
     * Gets the current value, which is the value associated with the last key
     * returned by <code>next()</code>.
     * 
     * @return the current value
     * @throws IllegalStateException
     *             if <code>next()</code> has not yet been called
     */
    Object getValue();

    // -----------------------------------------------------------------------
    /**
     * Removes the last returned key from the underlying <code>Map</code>
     * (optional operation).
     * <p>
     * This method can be called once per call to <code>next()</code>.
     * 
     * @throws UnsupportedOperationException
     *             if remove is not supported by the map
     * @throws IllegalStateException
     *             if <code>next()</code> has not yet been called
     * @throws IllegalStateException
     *             if <code>remove()</code> has already been called since the
     *             last call to <code>next()</code>
     */
    void remove();

    /**
     * Sets the value associated with the current key (optional operation).
     * 
     * @param value
     *            the new value
     * @return the previous value
     * @throws UnsupportedOperationException
     *             if setValue is not supported by the map
     * @throws IllegalStateException
     *             if <code>next()</code> has not yet been called
     * @throws IllegalStateException
     *             if <code>remove()</code> has been called since the last
     *             call to <code>next()</code>
     */
    Object setValue(Object value);

}