/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.commons.collections4;

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<String,Integer> it = map.mapIterator();
while (it.hasNext()) {
  String key = it.next();
  Integer value = it.getValue();
  it.setValue(value + 1);
 }

Type parameters:
<K> – the type of the keys in the map
<V> – the type of the values in the map
Since:
3.0/**
 * 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>
 * <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>
 * <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>.
 * </p>
 * <pre>{@code
 * MapIterator<String,Integer> it = map.mapIterator();
 * while (it.hasNext()) {
 *   String key = it.next();
 *   Integer value = it.getValue();
 *   it.setValue(value + 1);
 * }
 * }</pre>
 *
 * @param <K> the type of the keys in the map
 * @param <V> the type of the values in the map
 * @since 3.0
 */
public interface MapIterator<K, V> extends Iterator<K> {

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

    
Gets the next key from the Map.
Throws:
NoSuchElementException – if the iteration is finished
Returns:
the next key in the iteration/**
     * 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
     */
    @Override
    K next();

    //-----------------------------------------------------------------------
    
Gets the current key, which is the key returned by the last call
to next().
Throws:
IllegalStateException – if next() has not yet been called
Returns:
the current key/**
     * 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
     */
    K getKey();

    
Gets the current value, which is the value associated with the last key
returned by next().
Throws:
IllegalStateException – if next() has not yet been called
Returns:
the current value/**
     * 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
     */
    V 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
IllegalStateException – if next() has not yet been called
IllegalStateException – if remove() has already been called
 since the last call to next()/**
     * 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>
     */
    @Override
    void remove();

    
Sets the value associated with the current key (optional operation).
Params:
value –  the new value
Throws:
UnsupportedOperationException – if setValue is not supported by the map
IllegalStateException – if next() has not yet been called
IllegalStateException – if remove() has been called since the
 last call to next()
Returns:
the previous value/**
     * 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>
     */
    V setValue(V value);

}