    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4;
    018
    019import java.util.Iterator;
    020
    021/**
    022 * Defines an iterator that operates over a <code>Map</code>.
    023 * <p>
    024 * This iterator is a special version designed for maps. It can be more
    025 * efficient to use this rather than an entry set iterator where the option
    026 * is available, and it is certainly more convenient.
    027 * </p>
    028 * <p>
    029 * A map that provides this interface may not hold the data internally using
    030 * Map Entry objects, thus this interface can avoid lots of object creation.
    031 * </p>
    032 * <p>
    033 * In use, this iterator iterates through the keys in the map. After each call
    034 * to <code>next()</code>, the <code>getValue()</code> method provides direct
    035 * access to the value. The value can also be set using <code>setValue()</code>.
    036 * </p>
    037 * <pre>{@code
    038 * MapIterator<String,Integer> it = map.mapIterator();
    039 * while (it.hasNext()) {
    040 *   String key = it.next();
    041 *   Integer value = it.getValue();
    042 *   it.setValue(value + 1);
    043 * }
    044 * }</pre>
    045 *
    046 * @param <K> the type of the keys in the map
    047 * @param <V> the type of the values in the map
    048 * @since 3.0
    049 */
    050public interface MapIterator<K, V> extends Iterator<K> {
    051
    052    /**
    053     * Checks to see if there are more entries still to be iterated.
    054     *
    055     * @return <code>true</code> if the iterator has more elements
    056     */
    057    @Override
    058    boolean hasNext();
    059
    060    /**
    061     * Gets the next <em>key</em> from the <code>Map</code>.
    062     *
    063     * @return the next key in the iteration
    064     * @throws java.util.NoSuchElementException if the iteration is finished
    065     */
    066    @Override
    067    K next();
    068
    069    //-----------------------------------------------------------------------
    070    /**
    071     * Gets the current key, which is the key returned by the last call
    072     * to <code>next()</code>.
    073     *
    074     * @return the current key
    075     * @throws IllegalStateException if <code>next()</code> has not yet been called
    076     */
    077    K getKey();
    078
    079    /**
    080     * Gets the current value, which is the value associated with the last key
    081     * returned by <code>next()</code>.
    082     *
    083     * @return the current value
    084     * @throws IllegalStateException if <code>next()</code> has not yet been called
    085     */
    086    V getValue();
    087
    088    //-----------------------------------------------------------------------
    089    /**
    090     * Removes the last returned key from the underlying <code>Map</code> (optional operation).
    091     * <p>
    092     * This method can be called once per call to <code>next()</code>.
    093     *
    094     * @throws UnsupportedOperationException if remove is not supported by the map
    095     * @throws IllegalStateException if <code>next()</code> has not yet been called
    096     * @throws IllegalStateException if <code>remove()</code> has already been called
    097     *  since the last call to <code>next()</code>
    098     */
    099    @Override
    100    void remove();
    101
    102    /**
    103     * Sets the value associated with the current key (optional operation).
    104     *
    105     * @param value  the new value
    106     * @return the previous value
    107     * @throws UnsupportedOperationException if setValue is not supported by the map
    108     * @throws IllegalStateException if <code>next()</code> has not yet been called
    109     * @throws IllegalStateException if <code>remove()</code> has been called since the
    110     *  last call to <code>next()</code>
    111     */
    112    V setValue(V value);
    113
    114}