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+/*
+ * $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/java/org/apache/commons/collections/BidiMap.java,v 1.1 2003/09/20 20:24:30 scolebourne Exp $
+ * ====================================================================
+ *
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2001-2003 The Apache Software Foundation.  All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. The end-user documentation included with the redistribution, if
+ *    any, must include the following acknowledgement:
+ *       "This product includes software developed by the
+ *        Apache Software Foundation (http://www.apache.org/)."
+ *    Alternately, this acknowledgement may appear in the software itself,
+ *    if and wherever such third-party acknowledgements normally appear.
+ *
+ * 4. The names "The Jakarta Project", "Commons", and "Apache Software
+ *    Foundation" must not be used to endorse or promote products derived
+ *    from this software without prior written permission. For written
+ *    permission, please contact apache@apache.org.
+ *
+ * 5. Products derived from this software may not be called "Apache"
+ *    nor may "Apache" appear in their names without prior written
+ *    permission of the Apache Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.commons.collections;
+
+import java.util.Map;
+
+/**
+ * Defines a map that allows bidirectional lookup between key and values.
+ * <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.
+ *  
+ * @since Commons Collections 3.0
+ * @version $Revision: 1.1 $ $Date: 2003/09/20 20:24:30 $
+ *
+ * @author Stephen Colebourne
+ */
+public interface BidiMap extends Map {
+    
+    /**
+     * 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 specifed value is inappropriate
+     * @throws NullPointerException (optional) if the map limits the values to
+     *  non-null and null was specified
+     */
+    public 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</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 specifed 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
+     */
+    public Object removeKey(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
+     */
+    public BidiMap inverseBidiMap();
+    
+}