swing - Java Timer Not Working -

for reason java timer not working in 1 of programs. whenever compile code, gives me following error:

exception in thread "awt-eventqueue-0" java.lang.illegalstateexception:    task scheduled or cancelled      @ java.util.timer.sched(timer.java:401)      @ java.util.timer.scheduleatfixedrate(timer.java:328) 

why this? (note: novice @ java timers)

//timer prerequisites timer timer = new timer(); timertask task = new timertask() {     public void run()     {         system.out.println("we have waited 1 second.");     } };  //check see if user has enetered while(!answered) { timer.scheduleatfixedrate(task, 0, duration); afk = true; incorrect += 1; answered = true; }           

since noted in tag, should using swing timer, instead of using java.util.timer.

please have @ sample example:

import java.awt.*; import java.awt.event.*; import javax.swing.*;  public class swingtimerexample {      private string[] questions = {         "how you?",         "how day?",         "will work tonight?"     };      private jlabel questionlabel;     private buttongroup radiogroup;     private jradiobutton yesradiobutton;     private jradiobutton noradiobutton;      private int counter;      private static final int gap = 5;      private timer timer;      private actionlistener timeractions = new actionlistener () {         @override         public void actionperformed ( actionevent ae ) {             ++counter;             counter %= questions.length;             questionlabel.settext ( questions [ counter ] );             if ( counter == questions.length - 1 ) {                 ( ( timer ) ae.getsource () ).stop ();             }         }     };      public swingtimerexample () {         counter = 0;     }      private void displaygui () {         jframe frame = new jframe ( "swing timer example" );         frame.setdefaultcloseoperation ( jframe.dispose_on_close );          jpanel contentpane = new jpanel ();         contentpane.setborder ( borderfactory.createemptyborder (             gap, gap, gap, gap ) );         contentpane.setlayout ( new borderlayout ( gap, gap ) );          jpanel labelpanel = new jpanel ();         questionlabel = new jlabel (                              questions [ counter ], jlabel.center);         labelpanel.add ( questionlabel );          jpanel radiopanel = new jpanel ();         yesradiobutton = new jradiobutton ( "yes" );         noradiobutton = new jradiobutton ( "no" );         radiogroup = new buttongroup ();         radiogroup.add ( yesradiobutton );         radiogroup.add ( noradiobutton );         radiopanel.add ( yesradiobutton );         radiopanel.add ( noradiobutton );          contentpane.add ( labelpanel, borderlayout.center );         contentpane.add ( radiopanel, borderlayout.page_end );          frame.setcontentpane ( contentpane );         frame.pack ();         frame.setlocationbyplatform ( true );         frame.setvisible ( true );          timer = new timer ( 5000, timeractions );         timer.start ();     }      public static void main ( string[] args ) {         runnable runnable = new runnable () {             @override             public void run () {                 new swingtimerexample ().displaygui ();             }         };         eventqueue.invokelater ( runnable );     } }