Accessing Classes From Other Apk

I would like to know if it is possible to access directly a class in an apk from another apk. By example, in the notepad tutorial, an activity is launched by these lines of code:

Solution 1:

I have some sample code for you. Here you can start the clock-app of HTC smartphones

  Intent i = new Intent(Intent.ACTION_VIEW);
  i.setComponent(new ComponentName("com.htc.android.worldclock",
      "com.htc.android.worldclock.WorldClockTabControl"));
  startActivity(i);