더 간단한 코드

Handler_2.java

public class ThreadHandlerTest extends Activity {
    TextView tvTest;

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

        tvTest = (TextView) findViewById(R.id.tv_test);

        BackThread thread = new BackThread();
        thread.setDaemon(true); // 메인스레드와 같이 종료하기 위해서
        thread.start();
    }

    class BackThread extends Thread {
        @Override
        public void run() {
            val++;
            mHandler.post(new Runnable() {
                public void run() {
                    tvTest.setText(val + "");
                }
            });

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    Handler mHandler = new Handler();
}