java - Updating GUI through threads -

i'm new threads , haven't written java in long time bear me here. have simple gui. has counter, status label, , 2 buttons, start , stop respectively.

what wanted update status label using counter thread. when hit start supposedly starts counter @ 0 , increments every second, , when choose hit stop should suspend current thread , wait start button pressed again. whenever hit stop suspends waits second , resumes counting. when in reality want stay suspended. i'm not sure why it's doing that, tried searching before posting here got nothing. feel free criticize on you'd like.

here's have:

updated per @madprogrammer's answer.

import java.awt.font; import java.awt.gridbagconstraints; import java.awt.gridbaglayout; import java.awt.event.actionevent; import java.awt.event.actionlistener; import javax.swing.jbutton; import javax.swing.jframe; import static javax.swing.jframe.exit_on_close; import javax.swing.jlabel; import javax.swing.swingutilities;  public class main extends jframe  {       jlabel countlabel = new jlabel("0");     jlabel statuslabel = new jlabel("task not completed.");     jbutton startbutton = new jbutton("start");     jbutton stopbutton = new jbutton("stop");     counterthread worker = new counterthread("worker", countlabel, statuslabel);      public static void main(string[] args) {         swingutilities.invokelater(new runnable() {              @override             public void run() {                 new main("counter demo");             }         });     }      public main(string title) {         super(title);          setlayout(new gridbaglayout());          countlabel.setfont(new font("serif", font.bold, 28));          gridbagconstraints gc = new gridbagconstraints();          gc.fill = gridbagconstraints.none;          gc.gridx = 0;         gc.gridy = 0;         gc.weightx = 1;         gc.weighty = 1;         add(countlabel, gc);          gc.gridx = 0;         gc.gridy = 1;         gc.weightx = 1;         gc.weighty = 1;         add(statuslabel, gc);          gc.gridx = 0;         gc.gridy = 2;         gc.weightx = 1;         gc.weighty = 1;         add(startbutton, gc);          gc.gridx = 0;         gc.gridy = 3;         gc.weightx = 1;         gc.weighty = 1;         add(stopbutton, gc);          startbutton.addactionlistener(new actionlistener() {             public void actionperformed(actionevent arg0) {                 worker.start();                 //notify();             }         });         stopbutton.addactionlistener(new actionlistener() {             public void actionperformed(actionevent arg0) {                 worker.suspend();             }         });         setsize(200, 400);         setdefaultcloseoperation(exit_on_close);         setvisible(true);     }  public class counterthread implements runnable {      public thread t;     public string threadname;     boolean suspended = false;     jlabel countlabelname;     jlabel statuslabelname;      counterthread(string name, jlabel clabel, jlabel slabel) {         this.threadname = name;         this.countlabelname = clabel;         this.statuslabelname = slabel;     }      public void run() {         try {             // simulate doing useful.             (int = 0; <= 10; i++) {                 synchronized (this) {                     if (suspended)                      {                                      wait();                     }                 }                 final int count = i;                  swingutilities.invokelater(new runnable() {                     public void run() {                         countlabelname.settext(integer.tostring(count));                     }                 });                 thread.sleep(1000);             }         } catch (interruptedexception e) {         }          swingutilities.invokelater(new runnable() {             public void run() {                 statuslabelname.settext("completed.");             }         });          this.start();     }      public boolean getstatus() {         return t == null;     }      public void start() {         if (getstatus()) {             //t = new thread(new counterthread(this.threadname, this.countlabelname, this.statuslabelname));             t = new thread(this);             t.start();         }     }      public void suspend() {         statuslabelname.settext("task paused");         suspended = true;     }     //create object purpose synchronize      synchronized void resume() {         statuslabelname.settext("task has resumed");         suspended = false;         this.notify();     }  } } 

basically...

synchronized(this) {     if(suspended)     {         if(getstatus())             wait();         resume();     } } 

getstatus returning false it's skipping wait call (because t != null.

i'm not sure why need check this, might have enum or other flag returns more meaningful state (like running, stopped, paused ... ever)

i able make work doing like...

synchronized(this) {     if(suspended)     {         wait();     } } 

instead.

having said though. i'd consider using swing timer work , trigger it's updates within context of edt

updated after original code modified

even suggested answer it's still behaving same way, suspends brief second , resumes right away

you modified code original post, adding

t = new thread(new counterthread(this.threadname, this.countlabelname, this.statuslabelname)); 

to start method, ui code has reference counterthread it's interacting with, have 2 instances of same class, 1 running in background ticking away , 1 ui code interacting with.

so when ui calls suspend, it's not changing suspended state of instance running

import java.awt.font; import java.awt.gridbagconstraints; import java.awt.gridbaglayout; import java.awt.event.actionevent; import java.awt.event.actionlistener; import javax.swing.jbutton; import javax.swing.jframe; import static javax.swing.jframe.exit_on_close; import javax.swing.jlabel; import javax.swing.swingutilities;  public class main extends jframe {      jlabel countlabel = new jlabel("0");     jlabel statuslabel = new jlabel("task not completed.");     jbutton startbutton = new jbutton("start");     jbutton stopbutton = new jbutton("stop");     int holder;     counterthread worker = new counterthread("worker", countlabel, statuslabel);      public static void main(string[] args) {         swingutilities.invokelater(new runnable() {              @override             public void run() {                 new main("counter demo");             }         });     }      public main(string title) {         super(title);          setlayout(new gridbaglayout());          countlabel.setfont(new font("serif", font.bold, 28));          gridbagconstraints gc = new gridbagconstraints();          gc.fill = gridbagconstraints.none;          gc.gridx = 0;         gc.gridy = 0;         gc.weightx = 1;         gc.weighty = 1;         add(countlabel, gc);          gc.gridx = 0;         gc.gridy = 1;         gc.weightx = 1;         gc.weighty = 1;         add(statuslabel, gc);          gc.gridx = 0;         gc.gridy = 2;         gc.weightx = 1;         gc.weighty = 1;         add(startbutton, gc);          gc.gridx = 0;         gc.gridy = 3;         gc.weightx = 1;         gc.weighty = 1;         add(stopbutton, gc);          startbutton.addactionlistener(new actionlistener() {             public void actionperformed(actionevent arg0) {                 worker.start();             }          });          stopbutton.addactionlistener(new actionlistener() {             public void actionperformed(actionevent arg0) {                 worker.suspend();             }         });         setsize(200, 400);         setdefaultcloseoperation(exit_on_close);         setvisible(true);     }      public class counterthread implements runnable {          public thread t;         public string threadname;         boolean suspended = false;         jlabel countlabelname;         jlabel statuslabelname;          counterthread(string name, jlabel clabel, jlabel slabel) {             this.threadname = name;             this.countlabelname = clabel;             this.statuslabelname = slabel;         }          public void run() {             try {                 // simulate doing useful.                 (int = 0; <= 10; i++) {                     synchronized (this) {                         if (suspended) {                             wait();                         }                     }                     final int count = i;                      swingutilities.invokelater(new runnable() {                         public void run() {                             countlabelname.settext(integer.tostring(count));                         }                     });                      thread.sleep(1000);                  }             } catch (interruptedexception e) {             }              swingutilities.invokelater(new runnable() {                 public void run() {                     statuslabelname.settext("completed.");                 }             });              this.start();         }          public boolean getstatus() {             return t == null;         }          public void start() {             if (getstatus()) {                 //t = new thread(new counterthread(this.threadname, this.countlabelname, this.statuslabelname));                 t = new thread(this);                 t.start();             }         }          public void suspend() {             statuslabelname.settext("task paused");             suspended = true;         }         //create object purpose synchronize          synchronized void resume() {             statuslabelname.settext("task has resumed");             suspended = false;             this.notify();         }      } } 

also, don't see how using swing timer me in case, since there's no actual delay wait

then don't understand how timer works

import java.awt.font; import java.awt.gridbagconstraints; import java.awt.gridbaglayout; import java.awt.event.actionevent; import java.awt.event.actionlistener; import javax.swing.jbutton; import javax.swing.jframe; import static javax.swing.jframe.exit_on_close; import javax.swing.jlabel; import javax.swing.swingutilities; import javax.swing.timer;  public class main extends jframe {      jlabel countlabel = new jlabel("0");     jlabel statuslabel = new jlabel("task not completed.");     jbutton startbutton = new jbutton("start");     jbutton stopbutton = new jbutton("stop");     int holder;      timer timer;     int count = 0;      public static void main(string[] args) {         swingutilities.invokelater(new runnable() {              @override             public void run() {                 new main("counter demo");             }         });     }      public main(string title) {         super(title);          setlayout(new gridbaglayout());          countlabel.setfont(new font("serif", font.bold, 28));          gridbagconstraints gc = new gridbagconstraints();          gc.fill = gridbagconstraints.none;          gc.gridx = 0;         gc.gridy = 0;         gc.weightx = 1;         gc.weighty = 1;         add(countlabel, gc);          gc.gridx = 0;         gc.gridy = 1;         gc.weightx = 1;         gc.weighty = 1;         add(statuslabel, gc);          gc.gridx = 0;         gc.gridy = 2;         gc.weightx = 1;         gc.weighty = 1;         add(startbutton, gc);          gc.gridx = 0;         gc.gridy = 3;         gc.weightx = 1;         gc.weighty = 1;         add(stopbutton, gc);          timer = new timer(1000, new actionlistener() {             @override             public void actionperformed(actionevent e) {                 count++;                 countlabel.settext(integer.tostring(count));             }         });          startbutton.addactionlistener(new actionlistener() {             public void actionperformed(actionevent arg0) {                 timer.start();             }          });          stopbutton.addactionlistener(new actionlistener() {             public void actionperformed(actionevent arg0) {                 if (timer.isrunning()) {                     timer.stop();                     stopbutton.settext("resume");                 } else {                     timer.restart();                     stopbutton.settext("stop");                 }             }         });         setsize(200, 400);         setdefaultcloseoperation(exit_on_close);         setvisible(true);      } } 

now, there pause , resume issues taken care off