Can you explain how the handler (Handler) mechanism works in a system?

In Android, a Handler is used to manage a message queue and execute code in a specific thread, most often in the UI thread. It is associated with a Looper — an object that processes messages from the queue.

Working mechanism:

• The Handler receives messages or Runnable objects and places them into the Looper's message queue.
• The Looper sequentially retrieves messages from the queue and passes them to the Handler for processing.
• The Handler executes the code associated with the message in the thread where it was created.

This allows, for example, updating the UI from a background thread by sending messages to a Handler associated with the main thread.

Example:

Handler handler = new Handler(Looper.getMainLooper());

// Run code in the UI thread after 1 second
handler.postDelayed(() -> {
    // update UI
}, 1000);