What is the different between Handler, Runnable, and Threads?

Why use Runnable over Thread?

• Runnable separates code that needs to run asynchronously, from how the code is run. This keeps your code flexible. For instance, asynchronous code in a runnable can run on a threadpool, or a dedicated thread.

  A Thread has state your runnable probably doesn’t need access to. Having access to more state than necessary is poor design.

  Threads occupy a lot of memory. Creating a new thread for every small actions takes processing time to allocate and deallocate this memory.

What is runOnUiThread actually doing?

• Android’s runOnUiThread queues a Runnable to execute on the UI thread. This is important because you should never update UI from multiple threads. runOnUiThread uses a Handler.

  Be aware if the UI thread’s queue is full, or the items needing execution are lengthy, it may be some time before your queued Runnable actually runs.

What is a Handler?

• A handler allows you to post runnables to execute on a specific thread. Behind the scenes, runOnUi Thread queues your Runnable up with Android’s Ui Handler so your runnable can execute safely on the UI thread.