How can I show an inform JDialog before System.exit() in Java Swing? (Closed) -

in simple login window, added action listener login button. on pressing button, program check information user entered, if enter wrong info 3 times program create new jdialog inform user, after program shut down.

my problem jdialog appears blank program shutting down.

here code

btnlogin.addactionlistener(new actionlistener() {         @override         public void actionperformed(actionevent actionevent) {             char[] pass = psspassword.getpassword();             string pss = new string(pass);              if (!pss.tostring().equals("admin") || !txtusername.gettext().equals("adminuser")){                 if (attempts == 2){                     swingutilities.invokelater(new runnable() {                         @override                         public void run() {                             new inform("you entered wrong info 3 times, program shut down");                             try {                                 thread.sleep(1000);                                 system.exit(0);                             } catch (interruptedexception e) {                                 e.printstacktrace();                             }                         }                     });                    }else {                     swingutilities.invokelater(new runnable() {                         @override                         public void run() {                             new info("wrong info, please check info");                         }                     });                     attempts += 1;                 }             }else{              }         }     }); 

this inform class:

public class inform extends jdialog{  private jpanel pnlinform; private jlabel lblinform; private jbutton btnok;  public inform(string info){     setcontentpane(pnlinform);     lblinform.settext(info);     pack();     setvisible(true);     setdefaultcloseoperation(jdialog.dispose_on_close);     setlocationrelativeto(null);     btnok.addactionlistener(new actionlistener() {         @override         public void actionperformed(actionevent actionevent) {             dispose();         }     }); } 

}

my ide intellij idea , use form class create gui, there no declaration elements.

you didnt add components inform dialog since pnlinform not constructed , resolvs null , through contentpane cannot set null.
solutions : construct components (pnlinform,lblinform,btnok) , add them dialog. below can find full functioning code:

package test.q5;  import java.awt.event.actionevent; import java.awt.event.actionlistener;  import javax.swing.jbutton; import javax.swing.jdialog; import javax.swing.jlabel; import javax.swing.jpanel;  public class inform extends jdialog {      private jpanel pnlinform=new jpanel();     private jlabel lblinform=new jlabel();     private jbutton btnok=new jbutton("ok");      public inform(string info) { //      setcontentpane(pnlinform);         add(pnlinform);         lblinform.settext(info);         pnlinform.add(lblinform);         pnlinform.add(btnok);          pack();         setvisible(true);         setdefaultcloseoperation(jdialog.dispose_on_close);         setlocationrelativeto(null);         btnok.addactionlistener(new actionlistener() {             @override             public void actionperformed(actionevent actionevent) {                 dispose();             }         });     }      public static void main(string[] args) {         new inform("hello");     } } 

however , still need formatting message, please feel free add question able help.