What is Handler and what is it used for?

A Handler in Android is used to send and process messages and runnables on a specific thread's message queue. It allows you to interact with the main thread (also known as the UI thread) from a background thread, such as a worker thread or a separate process[1][3].

The main use cases for Handler are:

1. Updating the UI from a background thread: Since you cannot directly update the UI from a background thread, you can use a Handler to post UI updates to the main thread's message queue[1][4].

2. Scheduling delayed tasks or periodic work: A Handler can be used to schedule tasks to be executed at a specific time in the future or repeatedly at a fixed interval[5].

3. Communicating between threads: By posting messages to a Handler, you can safely pass data between threads and ensure thread-safe communication[3].

Here's how a Handler works:

1. A Handler is associated with a thread's message queue and the Looper that processes messages from that queue[3].

2. When you create a Handler, i...