how to clear application cache on exit ?

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Mobile

Android

i want to clear application cache memory and data on exit of application...
i used following code but it is not executed....please guide me..

@Override
 protected void onDestroy() {
      // TODO Auto-generated method stub
  super.onDestroy();
  Log.i("ondestroy", "message");
      try {

           trimCache(getApplicationContext());
        } catch (Exception e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
    }
  }

   public static void trimCache(Context context) {
          try {
              Log.i("trimcache", "message");

             File dir = context.getCacheDir();
             if (dir != null && dir.isDirectory()) {
                deleteDir(dir);
             }

          } catch (Exception e) {
             // TODO: handle exception
          }
       }



       public static boolean deleteDir(File dir) {
           Log.i("ondestry", "message");
          if (dir != null && dir.isDirectory()) {
             String[] children = dir.list();
             for (int i = 0; i <= children.length; i++) {
            boolean success = deleteDir(new File(dir, children[i]));
                if (!success) {
                   return false;
                }
             }
          }

          // The directory is now empty so delete it
          return dir.delete();
   }