Java 官網對Looper對象的說明：

public class Looperextends Object
Class used to run a message loop for a thread. Threads by default do not have a message loop associated with them; to create one, call prepare() in the thread that is to run the loop, and then loop() to have it process messages until the loop is stopped.

Most interaction with a message loop is through the Handler class.

This is a typical example of the implementation of a Looper thread, using the separation of prepare() and loop() to create an initial Handler to communicate with the Looper.

static void loop() ：  Run the message queue in this thread.
static void prepare() ：  Initialize the current thread as a looper.