/*

  * 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.el;

 import java.util.Collection;

 import java.util.Enumeration;

 import java.util.HashMap;

 import java.util.Map;

 import java.util.Set;

 /**

  *

  * <p>This is a Map implementation driven by a data source that only

  * provides an enumeration of keys and a getValue(key) method.  This

  * class must be subclassed to implement those methods.

  *

  * <p>Some of the methods may incur a performance penalty that

  * involves enumerating the entire data source.  In these cases, the

  * Map will try to save the results of that enumeration, but only if

  * the underlying data source is immutable.

  * 

  * @author Nathan Abramson - Art Technology Group

  * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: bayard $

  **/

 public abstract class EnumeratedMap

   implements Map

 {

   //-------------------------------------

   // Member variables

   //-------------------------------------

   Map mMap;

   //-------------------------------------

   public void clear ()

   {

     throw new UnsupportedOperationException ();

   }

   //-------------------------------------

   public boolean containsKey (Object pKey)

   {

     return getValue (pKey) != null;

   }

   //-------------------------------------

   public boolean containsValue (Object pValue)

   {

     return getAsMap ().containsValue (pValue);

   }

   //-------------------------------------

   public Set entrySet ()

   {

     return getAsMap ().entrySet ();

   }

   //-------------------------------------

   public Object get (Object pKey)

   {

     return getValue (pKey);

   }

   //-------------------------------------

   public boolean isEmpty ()

   {

     return !enumerateKeys ().hasMoreElements ();

   }

   //-------------------------------------

   public Set keySet ()

   {

     return getAsMap ().keySet ();

   }

   //-------------------------------------

   public Object put (Object pKey, Object pValue)

   {

     throw new UnsupportedOperationException ();

   }

   //-------------------------------------

   public void putAll (Map pMap)

   {

     throw new UnsupportedOperationException ();

   }

   //-------------------------------------

   public Object remove (Object pKey)

   {

     throw new UnsupportedOperationException ();

   }

   //-------------------------------------

   public int size ()

   {

     return getAsMap ().size ();

   }

   //-------------------------------------

   public Collection values ()

   {

     return getAsMap ().values ();

   }

   //-------------------------------------

   // Abstract methods

   //-------------------------------------

   /**

    *

    * Returns an enumeration of the keys

    **/

   public abstract Enumeration enumerateKeys ();

   //-------------------------------------

   /**

    *

    * Returns true if it is possible for this data source to change

    **/

   public abstract boolean isMutable ();

   //-------------------------------------

   /**

    *

    * Returns the value associated with the given key, or null if not

    * found.

    **/

   public abstract Object getValue (Object pKey);

   //-------------------------------------

   /**

    *

    * Converts the MapSource to a Map.  If the map is not mutable, this

    * is cached

    **/

   public Map getAsMap ()

   {

     if (mMap != null) {

       return mMap;

     }

     else {

       Map m = convertToMap ();

       if (!isMutable ()) {

         mMap = m;

       }

       return m;

     }

   }

   //-------------------------------------

   /**

    *

    * Converts to a Map

    **/

   Map convertToMap ()

   {

     Map ret = new HashMap ();

     for (Enumeration e = enumerateKeys (); e.hasMoreElements (); ) {

       Object key = e.nextElement ();

       Object value = getValue (key);

       ret.put (key, value);

     }

     return ret;

   }

   //-------------------------------------

 }