executor.java

ExecutorService executor = Executors.newSingleThreadExecutor();
Handler handler = new Handler(Looper.getMainLooper());

executor.execute(() -> {
    //Background work here
    handler.post(() -> {
        //UI Thread work here
    });
});

thread.java

new Thread(() -> {
    // do background stuff here
    runOnUiThread(()->{
        // OnPostExecute stuff here
    });
}).start();