Android Programming The Big Nerd Ranch Guide by Bill Phillips, Chris Stewart, Kristin Marsicano (z-lib.org)

Communicating with the Main Thread

In Android, the inbox that threads use is called a message queue. A thread that works by using a
message queue is called a message loop; it loops again and again looking for new messages on its
queue (Figure 26.3).

Figure 26.3  Flash dance

A message loop consists of a thread and a looper. The Looper is the object that manages a thread’s
message queue.

The main thread is a message loop and has a looper. Everything your main thread does is performed by
its looper, which grabs messages off of its message queue and performs the task they specify.

You are going to create a background thread that is also a message loop. You will use a class called
HandlerThread that prepares a Looper for you.