start_thread

public class MainActivity extends AppCompatActivity {

    private Runnable runnable = new Runnable() {
        @Override
        public void run() {
            // This runs in background thread. Do heavy operations here
        }
            // This thread will die once it comes out of the run method
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Thread thread = new Thread(runnable);
        thread.start();
    }
}