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Commons Collections example source code file (BidiMap.java)

This example Commons Collections source code file (BidiMap.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

bidimap, bidimap, iterablemap, iterablemap, mapiterator, mapiterator, object, object

The Commons Collections BidiMap.java source code

/*
 *  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.collections;

/**
 * Defines a map that allows bidirectional lookup between key and values.
 * <p>
 * This extended <code>Map represents a mapping where a key may
 * lookup a value and a value may lookup a key with equal ease.
 * This interface extends <code>Map and so may be used anywhere a map
 * is required. The interface provides an inverse map view, enabling
 * full access to both directions of the <code>BidiMap.
 * <p>
 * Implementations should allow a value to be looked up from a key and
 * a key to be looked up from a value with equal performance.
 * <p>
 * This map enforces the restriction that there is a 1:1 relation between
 * keys and values, meaning that multiple keys cannot map to the same value. 
 * This is required so that "inverting" the map results in a map without 
 * duplicate keys. See the {@link #put} method description for more information.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public interface BidiMap extends IterableMap {

    /**
     * Obtains a <code>MapIterator over the map.
     * <p>
     * A map iterator is an efficient way of iterating over maps.
     * It does not require that the map is stored using Map Entry objects
     * which can increase performance.
     * <pre>
     * BidiMap map = new DualHashBidiMap();
     * MapIterator it = map.mapIterator();
     * while (it.hasNext()) {
     *   Object key = it.next();
     *   Object value = it.getValue();
     *   it.setValue("newValue");
     * }
     * </pre>
     * 
     * @return a map iterator
     */
    MapIterator mapIterator();
    
    /**
     * Puts the key-value pair into the map, replacing any previous pair.
     * <p>
     * When adding a key-value pair, the value may already exist in the map
     * against a different key. That mapping is removed, to ensure that the
     * value only occurs once in the inverse map.
     * <pre>
     *  BidiMap map1 = new DualHashBidiMap();
     *  map.put("A","B");  // contains A mapped to B, as per Map
     *  map.put("A","C");  // contains A mapped to C, as per Map
     * 
     *  BidiMap map2 = new DualHashBidiMap();
     *  map.put("A","B");  // contains A mapped to B, as per Map
     *  map.put("C","B");  // contains C mapped to B, key A is removed
     * </pre>
     *
     * @param key  the key to store
     * @param value  the value to store
     * @return the previous value mapped to this key
     * 
     * @throws UnsupportedOperationException if the <code>put method is not supported
     * @throws ClassCastException (optional) if the map limits the type of the 
     *  value and the specified value is inappropriate
     * @throws IllegalArgumentException (optional) if the map limits the values
     *  in some way and the value was invalid
     * @throws NullPointerException (optional) if the map limits the values to
     *  non-null and null was specified
     */
    Object put(Object key, Object value);
    
    /**
     * Gets the key that is currently mapped to the specified value.
     * <p>
     * If the value is not contained in the map, <code>null is returned.
     * <p>
     * Implementations should seek to make this method perform equally as well
     * as <code>get(Object).
     *
     * @param value  the value to find the key for
     * @return the mapped key, or <code>null if not found
     * 
     * @throws ClassCastException (optional) if the map limits the type of the 
     *  value and the specified value is inappropriate
     * @throws NullPointerException (optional) if the map limits the values to
     *  non-null and null was specified
     */
    Object getKey(Object value);
    
    /**
     * Removes the key-value pair that is currently mapped to the specified
     * value (optional operation).
     * <p>
     * If the value is not contained in the map, <code>null is returned.
     * <p>
     * Implementations should seek to make this method perform equally as well
     * as <code>remove(Object).
     *
     * @param value  the value to find the key-value pair for
     * @return the key that was removed, <code>null if nothing removed
     * 
     * @throws ClassCastException (optional) if the map limits the type of the 
     *  value and the specified value is inappropriate
     * @throws NullPointerException (optional) if the map limits the values to
     *  non-null and null was specified
     * @throws UnsupportedOperationException if this method is not supported
     *  by the implementation
     */
    Object removeValue(Object value);
    
    /**
     * Gets a view of this map where the keys and values are reversed.
     * <p>
     * Changes to one map will be visible in the other and vice versa.
     * This enables both directions of the map to be accessed as a <code>Map.
     * <p>
     * Implementations should seek to avoid creating a new object every time this
     * method is called. See <code>AbstractMap.values() etc. Calling this
     * method on the inverse map should return the original.
     *
     * @return an inverted bidirectional map
     */
    BidiMap inverseBidiMap();
    
}

Other Commons Collections examples (source code examples)

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