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package org.apache.taglibs.standard.lang.jstl;

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: tcfujii $
 **/

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;
  }

  //-------------------------------------
}