Handler related issues

Which class does handler belong to?
Handler, Looper, MessageQueue when to establish the interrelationship?
When were the Looper and MessageQueue of the main thread created?
In the same thread, what is the number correspondence between Looper and MessageQueue, and what is the number correspondence with handler?
MessageQueue message is empty, thread blocking hangs wait, why not cause ANR?
What is the memory leak about handler?

Handler related issues