java - Continuing a loop until good input? -

i'm trying make program user needs account access other parts of it. want set if user's 2 confirm password dont match, have reenter info. also, if user leaves blank, must reenter info. how can continues loop until user enters info?

if (e.getsource() == okbutton) {         if(!passstring.equals(passstringconfirm) || username.equals(null) || passstring.equals(null) || passstringconfirm.equals(null)){                 enterusername.settext("");                 enterpassword.settext("");                 enterconfirmpassword.settext("");                 }             } 

this have far, , if works 1 iteration. tried while , continually print out warning message trying print out in joptionpane.

import java.awt.color; import java.awt.flowlayout; import java.awt.event.actionevent; import java.awt.event.actionlistener;  import javax.swing.borderfactory; import javax.swing.jbutton; import javax.swing.jframe; import javax.swing.jlabel; import javax.swing.joptionpane; import javax.swing.jpasswordfield; import javax.swing.jtextfield; import javax.swing.border.border;  public class createaccount extends jframe implements actionlistener {      jlabel username = new jlabel("enter username");     jtextfield enterusername = new jtextfield(null, 15);     jlabel password = new jlabel("enter password");     jpasswordfield enterpassword = new jpasswordfield(null, 15);     jlabel passwordconfirm = new jlabel("confirm password.");     jpasswordfield enterconfirmpassword = new jpasswordfield(null, 15);     jbutton okbutton = new jbutton("ok");      string username;     double initialdeposit;      public createaccount() {          add(username);         add(enterusername);         add(password);         add(enterpassword);         add(passwordconfirm);         add(enterconfirmpassword);         add(okbutton);          okbutton.addactionlistener(this);          settitle("new bank account creation");         setvisible(true);         setlocationrelativeto(null);         setsize(270, 300);         setdefaultcloseoperation(exit_on_close);         setlayout(new flowlayout());      }      @override     public void actionperformed(actionevent e) {          char[] pass = enterpassword.getpassword();         string passstring = new string(pass);         char[] passconfirm = enterconfirmpassword.getpassword();         string passstringconfirm = new string(passconfirm);          username = enterusername.gettext();          if (e.getsource() == okbutton) {             if(username == null || username.isempty() || passstring == null || passstring.isempty() || !passstring.equals(passstringconfirm)) {                     enterusername.settext("");                     enterpassword.settext("");                     enterconfirmpassword.settext("");                     border redline = borderfactory.createlineborder(color.red);                     enterusername.setborder(redline);                     enterpassword.setborder(redline);                     enterconfirmpassword.setborder(redline);                     repaint();                     }                 }             super.dispose();              int response = 0;             string firstdesposit = joptionpane.showinputdialog("welcome " + username + ". enter initial deposit.");             initialdeposit = double.parsedouble(firstdesposit);             if (response == joptionpane.ok_option) {                 new menu();             }         }     } 

your if test cannot correct. if of string(s) null nullpointerexception. think wanted

if (username == null || username.isempty() || passstring == null             || passstring.isempty()             || !passstring.equals(passstringconfirm)) {     enterusername.settext("");     enterpassword.settext("");     enterconfirmpassword.settext(""); } 

then ui code should check if empty before allowing user proceed. finally, in code above believe might use setborder() give fields red border.

if (username == null || username.isempty() || passstring == null             || passstring.isempty()             || !passstring.equals(passstringconfirm)) {     border redline = borderfactory.createlineborder(color.red);     enterusername.settext("");     enterpassword.settext("");     enterconfirmpassword.settext("");     enterusername.setborder(redline);     enterpassword.setborder(redline);     enterconfirmpassword.setborder(redline); } 

edit

based on code provided, need in else!

if(username == null || username.isempty() || passstring == null         || passstring.isempty() || !passstring.equals(passstringconfirm)) {     enterusername.settext("");     enterpassword.settext("");     enterconfirmpassword.settext("");     border redline = borderfactory.createlineborder(color.red);     enterusername.setborder(redline);     enterpassword.setborder(redline);     enterconfirmpassword.setborder(redline);     repaint(); } else { // <-- add     super.dispose();     int response = 0;     string firstdesposit = joptionpane.showinputdialog(             "welcome " + username + ". enter initial deposit.");     initialdeposit = double.parsedouble(firstdesposit);     if (response == joptionpane.ok_option) {         new menu();     } }