public class MainActivity extends Activity
{
int min, sec;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    min = 5;
    sec = 0;
    final TextView timer1 = (TextView) findViewById(R.id.timer1);
    timer1.setText(min + ":" + sec);
    Thread t = new Thread() {
        public void run() {
                sec-=1;
                if (sec<0) {
                    min-=1;
                    sec=59;
                }
                timer1.setText(min + ":" + sec);
                try
                {
                    sleep(1000);
                }
                catch (InterruptedException e)
                {}
            }
    };
    t.start();
}
}

This is a code for a Thread in Java but it doesn't work. Can you help me?

Its a Timer that counts down from 5 Minutes to 0:00.

Solution 1

In your case you are using threads. So you cannot update ui from the thread other than the ui thread. SO you use runOnUithread. I would suggest you to use a countdown timer or a Handler.

1.CountDownTimer

http://developer.android.com/reference/android/os/CountDownTimer.html

Here's a link to another example. Suggest you to check the link for the count down timer.

Countdowntimer in minutes and seconds

Example:

 public class MainActivity extends Activity {

Button b; 
TextView tv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    tv = (TextView) findViewById(R.id.textView1);
    b= (Button) findViewById(R.id.button1);
    b.setOnClickListener(new OnClickListener()
    {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            startTimer(200000); 
        }

    });
}
private void startTimer(long time){
    CountDownTimer counter = new CountDownTimer(30000, 1000){
        public void onTick(long millisUntilDone){

           Log.d("counter_label", "Counter text should be changed");
          tv.setText("You have " + millisUntilDone + "ms");                    
        }

        public void onFinish() {
            tv.setText("DONE!");

        }
    }.start();
}
 }

2.You can use a Handler

Example :

Handler m_handler;
Runnable m_handlerTask ; 
int timeleft=100;
m_handler = new Handler(); 
m_handlerTask = new Runnable() 
{ 
@Override
public void run() {
if(timeleft>=0)
{  
     // do stuff
     Log.i("timeleft",""+timeleft);
     timeleft--; 
}      
else
{
  m_handler.removeCallbacks(m_handlerTask); // cancel run
} 
  m_handler.postDelayed(m_handlerTask, 1000); 
 }
 };
 m_handlerTask.run();     

3.Timer

Timer runs on a different thread. You should update ui on the ui thread. use runOnUiThread

Example :

  int timeleft=100;
  Timer _t = new Timer();  
  _t.scheduleAtFixedRate( new TimerTask() {
            @Override
            public void run() {

               runOnUiThread(new Runnable() //run on ui thread
                 {
                  public void run() 
                  { 
                    Log.i("timeleft",""+timeleft);  
                    //update ui

                  }
                 });
                 if(timeleft>==0)
                 { 
                 timeleft--; 
                 } 
                 else
                 {
                 _t.cancel();
                 }
            }
        }, 1000, 1000 ); 

Solution 2

You are trying to update the UI Thread from a background Thread with

timer1.setText(

which you can't do. You need to use runOnUiThread(), AsyncTask, CountDownTimer, or something similar.

See this answer for an example of runOnUiThread()

But CountDownTimer is nice for things like this.

Also, when posting a question on SO, statements like "it doesn't work." are very vague and often unhelpful. Please indicate the expected results compared to actual results of your code and logcat if the app is crashing.