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HandlerThreads and communication between Threads

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As Handlers are used to send Messages and Runnables to a Thread’s message queue it’s easy to implement event based communication between multiple Threads. Every Thread that has a Looper is able to receive and process messages. A HandlerThread is a Thread that implements such a Looper, for example the main Thread (UI Thread) implements the features of a HandlerThread.

Creating a Handler for the current Thread 

Handler handler = new Handler();

Creating a Handler for the main Thread (UI Thread) 

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

Send a Runnable from another Thread to the main Thread 

new Thread(new Runnable() {
    public void run() {
        // this is executed on another Thread

        // create a Handler associated with the main Thread
        Handler handler = new Handler(Looper.getMainLooper());

        // post a Runnable to the main Thread
        handler.post(new Runnable() {
            public void run() {
                // this is executed on the main Thread
            }
        });
    }
}).start();

Creating a Handler for another HandlerThread and sending events to it 

// create another Thread
HandlerThread otherThread = new HandlerThread("name");

// create a Handler associated with the other Thread
Handler handler = new Handler(otherThread.getLooper());

// post an event to the other Thread
handler.post(new Runnable() {
    public void run() {
        // this is executed on the other Thread
    }
});
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Handler:
* Handler
* HandlerThreads and communication between Threads
* Use Handler to create a Timer similar to javax.swing.Timer
* Using a Handler to execute code after a delayed amount of time
* Stop handler from execution
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