From API docs,
public final boolean sendEmptyMessage (int what)
Since: API Level 1
Sends a Message containing only the what value.
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting.
I am reading 'Android in Action' book, and below is the code excerpt. Though we are passing 0, but we are not utilizing it anywhere (atleast not that I am aware of). and that is how the question arose.