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/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2003-2004 The Apache Software Foundation.  All rights
 * reserved.
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 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
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 * .
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package org.apache.commons.collections;

import java.util.Iterator;

/**
 * Defines an iterator that operates over a Map.
 * 
 * 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.
 * 

 * 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.
 * 

 * In use, this iterator iterates through the keys in the map. After each call
 * to next(), the getValue() method provides direct
 * access to the value. The value can also be set using setValue().
 * 
 * MapIterator it = map.mapIterator();
 * while (it.hasNext()) {
 *   Object key = it.next();
 *   Object value = it.getValue();
 *   it.setValue(newValue);
 * }
 * 
 *  
 * @since Commons Collections 3.0
 * @version $Revision: 1.6 $ $Date: 2004/01/14 21:43:03 $
 *
 * @author Stephen Colebourne
 */
public interface MapIterator extends Iterator {
    
    /**
     * Checks to see if there are more entries still to be iterated.
     *
     * @return true if the iterator has more elements
     */
    boolean hasNext();

    /**
     * Gets the next key from the Map.
     *
     * @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 next().
     *
     * @return the current key
     * @throws IllegalStateException if next() has not yet been called
     */
    Object getKey();

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

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

}