org.apache.commons.collections15.BidiMap.java Source code

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// GenericsNote: Converted.
/*
 *  Copyright 2003-2004 The Apache Software Foundation
 *
 *  Licensed 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.collections15;

import java.util.Set;

/**
 * Defines a map that allows bidirectional lookup between key and values.
 * <p/>
 * This extended <code>Map</code> 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</code> 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</code>.
 * <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.
 *
 * @author Matt Hall, John Watkinson, Stephen Colebourne
 * @version $Revision: 1.1 $ $Date: 2005/10/11 17:05:19 $
 * @since Commons Collections 3.0
 */
public interface BidiMap<K, V> extends IterableMap<K, V> {

    /**
     * Obtains a <code>MapIterator</code> 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<K, V> 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
     * <p/>
     *  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</code> 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
     */
    V put(K key, V value);

    /**
     * Gets the key that is currently mapped to the specified value.
     * <p/>
     * If the value is not contained in the map, <code>null</code> is returned.
     * <p/>
     * Implementations should seek to make this method perform equally as well
     * as <code>get(Object)</code>.
     *
     * @param value the value to find the key for
     * @return the mapped key, or <code>null</code> 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
     */
    K 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</code> is returned.
     * <p/>
     * Implementations should seek to make this method perform equally as well
     * as <code>remove(Object)</code>.
     *
     * @param value the value to find the key-value pair for
     * @return the key that was removed, <code>null</code> 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
     */
    K 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</code>.
     * <p/>
     * Implementations should seek to avoid creating a new object every time this
     * method is called. See <code>AbstractMap.values()</code> etc. Calling this
     * method on the inverse map should return the original.
     *
     * @return an inverted bidirectional map
     */
    BidiMap<V, K> inverseBidiMap();

    /**
     * Returns a set view of the values contained in this BidiMap.  The
     * set is backed by the map, so changes to the map are reflected in
     * the collection, and vice-versa.  If the map is modified while an
     * iteration over the collection is in progress (except through the
     * iterator's own <tt>remove</tt> operation), the results of the
     * iteration are undefined.  The collection supports element removal,
     * which removes the corresponding mapping from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations.
     * It does not support the add or <tt>addAll</tt> operations.
     *
     * @return a Set view of the values contained in this map.
     */
    Set<V> values();

}