import java.util.Hashtable;

public class DefaultMemoDatabase implements MemoDatabase
{
  private Hashtable associations;
  
  public DefaultMemoDatabase()
  {
    associations = new Hashtable();
  }
  
  public boolean insert( MemoAssociation newEntry )
  {
    if ( containsKey( newEntry.key() ) )
      return false;
    
    associations.put( newEntry.key(), newEntry.value() );
    return true;
  }
  
  public String find( String key )
  {
    if ( containsKey( key ) )
      return (String) associations.get( key );     // why the cast?
    
    return null;
  }
  
  public boolean remove( String key )
  {
    if ( containsKey( key ) )
    {
      associations.remove( key );
      return true;
    }
    
    return false;
  }
  
  public boolean containsKey( String key )
  {
    return associations.containsKey( key );
  }
}