Android实现显示系统实时时间

<TextView
        android:id="@+id/real_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-- --"
        />

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        real_time=findViewById(R.id.real_time);
        Startthread();
    }
 //开启一个子线程
  private void Startthread(){
        new Thread(){
            @Override
            public void run() {
                do {
                    try {
                        Thread.sleep(1000);
                        Message message=new Message();
                        message.what=1;
                        handler.sendMessage(message);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }while (true);
            }
        }.start();
     }

//在主线程中进行数据处理
    private Handler handler=new Handler(){
        @Override
        public void handleMessage(@NonNull Message msg) {
            switch (msg.what){
                case 1:
                    long time = System.currentTimeMillis();
                    CharSequence fORMat = DateFormat.format("hh:mm:ss yyyy-MM-dd", time);
                    real_time.setText(format);
                    break;
            }
        }
    };