I tried by changing the IEnumFeature to MapSelection . My Code Looks like this---                               public void mousePressed(MouseEvent me) {
        try
        {
          mxDoc = (IMxDocument) app.getDocument();
          IActiveView pactiveView = mxDoc.getActivatedView();
          IMap pMap = pactiveView.getFocusMap();
          MapSelection iefeature = (MapSelection) pMap.getFeatureSelection();
          IFeature ifeature = iefeature.next();
          while(ifeature != null)
          {
          int oid = ifeature.getOID();
          list.add(oid);
          ifeature = iefeature.next();
          }
         JOptionPane.showMessageDialog(null,"Found :"+ list.size());
          mxDoc.getActiveView().refresh();
        }
        catch(Exception ex)
        {
          ex.printStackTrace();
          JOptionPane.showMessageDialog(null, "Error :"+ex);
        }
        }But i am receiving error again as follows--- [ATTACH=CONFIG]25606[/ATTACH]