java - What's the omission/error out here? -

there should error/omission in next code can't see because i've never used threads. can please find i'm missing?

import java.awt.borderlayout; import java.awt.button; import java.awt.event.actionevent; import java.awt.event.actionlistener; import java.util.timer; import java.util.timertask;  import javax.swing.jdialog; import javax.swing.jlabel;  public class javaswingtest extends jdialog {     private jlabel m_countlabel;      private timer m_timer = new timer();      private class incrementcounttask extends timertask {         @override         public void run() {             m_countlabel.settext(long.tostring(system.currenttimemillis()  / 1000));         }     }      private javaswingtest() {         createui();          m_timer.schedule(new incrementcounttask(), 1000, 1000);     }      private void createui() {         button button1 = new button("action1");         button1.addactionlistener(new actionlistener() {             @override             public void actionperformed(actionevent arg0) {                 dolongoperation();             }          });         add(button1, borderlayout.north);          m_countlabel = new jlabel(long.tostring(system.currenttimemillis()  / 1000));         add(m_countlabel, borderlayout.center);     }      /**      * simulates operation takes time complete.      */     private void dolongoperation() {         try {             thread.sleep(3000);         } catch (interruptedexception e) {             // ignored test         }     }      /**      * @param args      */     public static void main(string[] args) {         new javaswingtest().setvisible(true);     } } 

swing, ui toolkits, not thread-safe. settext() call should forwarded event thread.

to initiate gui work timer thread, use swingutilities.invokelater() or invokeandwait().