Intent intent = new Intent(); 
intent.setClassName(<package name>, <class name>); 
startActivity(intent);

Intent i=new Intent;
ComponentName com= new ComponentName(<Package Name> , <Calss Name>); 
i.setComponent(com); 
startActivity(i); 

Intent i = new Intent();

ComponentName comp = new ComponentName("com.Android.camera","com.android.camera.GalleryPicker");

i.setComponent(comp);

i.setAction("android.intent.action.VIEW");

startActivity(i);

Intent mIntent = new Intent();

ComponentName comp = new ComponentName("com.android.camera","com.android.camera.Camera");

mIntent.setComponent(comp);

mIntent.setAction("android.intent.action.VIEW");

startActivity(mIntent);

Intent intent = new Intent();

ComponentName cn = new ComponentName("com.android.htmlviewer", "com.android.htmlviewer.HTMLViewerActivity");

intent.setComponent(cn);

Uri uri = Uri.fromFile(new File("/sdcard/demo.txt"));

intent.setDataAndType(uri, "text/plain");

startActivity(intent);