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 */
017 package org.apache.commons.collections;
018
019 import 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 * A map that provides this interface may not hold the data internally using
029 * Map Entry objects, thus this interface can avoid lots of object creation.
030 * <p>
031 * In use, this iterator iterates through the keys in the map. After each call
032 * to <code>next()</code>, the <code>getValue()</code> method provides direct
033 * access to the value. The value can also be set using <code>setValue()</code>.
034 * <pre>
035 * MapIterator it = map.mapIterator();
036 * while (it.hasNext()) {
037 * Object key = it.next();
038 * Object value = it.getValue();
039 * it.setValue(newValue);
040 * }
041 * </pre>
042 *
043 * @since Commons Collections 3.0
044 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
045 *
046 * @author Stephen Colebourne
047 */
048 public interface MapIterator extends Iterator {
049
050 /**
051 * Checks to see if there are more entries still to be iterated.
052 *
053 * @return <code>true</code> if the iterator has more elements
054 */
055 boolean hasNext();
056
057 /**
058 * Gets the next <em>key</em> from the <code>Map</code>.
059 *
060 * @return the next key in the iteration
061 * @throws java.util.NoSuchElementException if the iteration is finished
062 */
063 Object next();
064
065 //-----------------------------------------------------------------------
066 /**
067 * Gets the current key, which is the key returned by the last call
068 * to <code>next()</code>.
069 *
070 * @return the current key
071 * @throws IllegalStateException if <code>next()</code> has not yet been called
072 */
073 Object getKey();
074
075 /**
076 * Gets the current value, which is the value associated with the last key
077 * returned by <code>next()</code>.
078 *
079 * @return the current value
080 * @throws IllegalStateException if <code>next()</code> has not yet been called
081 */
082 Object getValue();
083
084 //-----------------------------------------------------------------------
085 /**
086 * Removes the last returned key from the underlying <code>Map</code> (optional operation).
087 * <p>
088 * This method can be called once per call to <code>next()</code>.
089 *
090 * @throws UnsupportedOperationException if remove is not supported by the map
091 * @throws IllegalStateException if <code>next()</code> has not yet been called
092 * @throws IllegalStateException if <code>remove()</code> has already been called
093 * since the last call to <code>next()</code>
094 */
095 void remove();
096
097 /**
098 * Sets the value associated with the current key (optional operation).
099 *
100 * @param value the new value
101 * @return the previous value
102 * @throws UnsupportedOperationException if setValue is not supported by the map
103 * @throws IllegalStateException if <code>next()</code> has not yet been called
104 * @throws IllegalStateException if <code>remove()</code> has been called since the
105 * last call to <code>next()</code>
106 */
107 Object setValue(Object value);
108
109 }