while loop - Simple calculator in java - using boolean to ask if user wants to continue -

i writing basic calculator program in java using joptionpane. new , have received far appreciated!

my program suppose ask users number, has them select operator use (+,-,*,/,%) , asks users second number. after this, calculation performed , result displayed.

i have working code loops calculator once calculation done, users asked if use again. code works adjust when user asked if want continue , yes, instead of loop going , having input box "welcome calculator!\nplease enter first number:") i'd "please enter first number:" , keep going (since user not need welcomed again).

public static void main(string[] args) {     double numone; //first number float     double numtwo; //second number float     double result; //result of equation     string num1; //first number string     string num2; //second number string     string input; //operator type (+,-,*,/,%)     boolean usecalculator = false; //false quit, true use      while (!usecalculator) {         num1 = joptionpane.showinputdialog(null, "welcome calculator!\nplease enter first number:");         numone = double.parsedouble(num1);          input = joptionpane.showinputdialog(null, "thank you! do?\nplease choose following options:\n+\n-\n*\n%\n/");         while (input == null || !(input.equals("+") || input.equals("*") || input.equals("/") || input.equals("-"))) {             input = joptionpane.showinputdialog(null, "the operator invalid. please select correct operator.\nplease choose following options:\n+\n-\n*\n%\n/");         }         num2 = joptionpane.showinputdialog(null, "thank you!\nplease enter second number:");         numtwo = double.parsedouble(num2);     } } 

and

public static boolean askyesnoquestion(string prompt) {     string confirmationinput;     boolean repeat = false; //false quite calc, true repeat use of calc      while (true) {         confirmationinput = joptionpane.showinputdialog(null,                 prompt + " (please answer yes or no)");          if (confirmationinput.equalsignorecase("y") || confirmationinput.equalsignorecase("yes")) {             prompt = "please enter first number";             return true;         } else if (confirmationinput.equalsignorecase("n") || confirmationinput.equalsignorecase("no")) {             joptionpane.showmessagedialog(null, "you have decided quit calculator program.\n goodbye!");             return false;         }          if (!repeat) {             prompt = "that invalid choice. " + prompt;             repeat = true;         }     } } 

same other questions, want understand , learn how this. have added part of code clarity (i can add whole thing if needed) looking explanation on how accomplish can try out on own , work way through it. apologize if broad, i'd happy clear if needed! :)

@ajb hi everyone- have tried removing putting in changes (adding while loop , removing prompts) getting return error. have tried , finding has main method using void, unsure how fix this. if has further tips on new code below (so can again try , work through it), appreciate it!

import javax.swing.joptionpane;  public class test {      public static void main(string[] args) {         double numone; //first number float         double numtwo; //second number float         double result; //result of equation         string num1; //first number string         string num2; //second number string         string input; //operator type (+,-,*,/,%)         string confirmationinput;         boolean useagain = false;         boolean usecalculator = false; //false if user decides quit, true if user continues use calculator           while (!usecalculator) {             num1 = joptionpane.showinputdialog(null, "welcome calculator!\nplease enter first number:");             numone = double.parsedouble(num1);              input = joptionpane.showinputdialog(null, "thank you! do?\nplease choose following options:\n+\n-\n*\n%\n/");              //while loop gathers user input. asks user repeatedly until valid operator entered             while (input == null || !(input.equals("+") || input.equals("*") || input.equals("/") || input.equals("-") || input.equals("%"))) {                 input = joptionpane.showinputdialog(null, "the operator " + input + "  invalid. please select correct operator.\nplease choose following options:\n+\n-\n*\n%\n/");             }             num2 = joptionpane.showinputdialog(null, "thank you!\nplease enter second number:");             numtwo = double.parsedouble(num2);              //calculates result of user input based on operator choosen             if (input != null && input.equals("+")) {                 add(numone, numtwo);                 result = add(numone, numtwo);                 joptionpane.showmessagedialog(null, "the result of " + numone + " " + input + " " + numtwo + " is: " + result);             } else if (input != null && input.equals("-")) {                 minus(numone, numtwo);                 result = minus(numone, numtwo);                 joptionpane.showmessagedialog(null, "the result of " + numone + " " + input + " " + numtwo + " is: " + result);             } else if (input != null && input.equals("*")) {                 multiply(numone, numtwo);                 result = multiply(numone, numtwo);                 joptionpane.showmessagedialog(null, "the result of " + numone + " " + input + " " + numtwo + " is: " + result);             } else if (input != null && input.equals("/")) {                 divide(numone, numtwo);                 result = divide(numone, numtwo);                 joptionpane.showmessagedialog(null, "the result of " + numone + " " + input + " " + numtwo + " is: " + result);             } else if (input != null && input.equals("%")) {                 modul(numone, numtwo);                 result = modul(numone, numtwo);                 joptionpane.showmessagedialog(null, "the result of " + numone + " " + input + " " + numtwo + " is: " + result);             }              if (!usecalculator) {               joptionpane.showinputdialog(null, "would continue using calculator? (please answer yes or no)"); while (true) {              if (confirmationinput.equalsignorecase("y") || confirmationinput.equalsignorecase("yes")) {                 num1 = joptionpane.showinputdialog(null, "please enter first number:");                 return true;             } else if (confirmationinput.equalsignorecase("n") || confirmationinput.equalsignorecase("no")) {                 joptionpane.showmessagedialog(null, "you have decided quit calculator program.\n goodbye!");                 return false;             }              if (!useagain) {                 joptionpane.showinputdialog(null, "that invalid choice.\nwould continue using calculator? (please answer yes or no)");                  useagain = true;             } }             }           system.out.println("end of calculator program. program completed successfully");     }     }