Thomas VanHuy

Joanne Neal wrote:

Thomas VanHuy wrote:I can enter the operation, then I click "ok" to go to the next box but my program closes after clicking "ok".

Does it actually close or does it just sit there apparently doing nothing ?
On line 20 the program is waiting for you to input something on the command line. You don't need to do this. The name variable on line 18 contains the value you typed into the dialog. Get rid of all the Scanner objects you create and it should work fine.

Edit: You will of course need to convert the values of the option and option2 variables to doubles before you can use them in any arithmetic. You can use the Double.parseDouble method to do this.

Is this what you meant?

import javax.swing.JFrame; import javax.swing.JOptionPane; public class rekenmachine1 { public static void main(String[] args) { JFrame frame = new JFrame("Calculator"); String operand = null; double num1 = 0; double num2 = 0; double total; String name = JOptionPane.showInputDialog(frame,"Choose a function: +, -, /, *" ); if (operand.equals("+")) { String option = JOptionPane.showInputDialog(frame,"Enter the first number of the sum" ); Double option3 = new Double(option); String option2 = JOptionPane.showInputDialog(frame,"Enter the second number of the sum" ); Double option4 = new Double(option2); total = num1 + num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else if (operand.equals("-")) { String option = JOptionPane.showInputDialog(frame,"Enter the first number of the subtraction" ); Double option3 = new Double(option); String option2 = JOptionPane.showInputDialog(frame,"Enter the second number of the subtraction" ); Double option4 = new Double(option); total = num1 - num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else if(operand.equals("/")){ String option = JOptionPane.showInputDialog(frame,"Enter the number you wish to divide" ); Double option3 = new Double(option); String option2 = JOptionPane.showInputDialog(frame,"Enter the number you wish to divide the first number by" ); Double option4 = new Double(option); total = num1 / num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else if (operand.equals("*")) { String option = JOptionPane.showInputDialog(frame,"Enter the number you wish to multiply" ); Double option3 = new Double(option); String option2 = JOptionPane.showInputDialog(frame,"Enter the number you wish to multiply the first number by" ); Double option4 = new Double(option); total = num1 * num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else { JOptionPane.showMessageDialog(frame, "Oops, something went wrong, try again."); } } }

Because now after entering the operation I get this exception: Exception in thread "main" java.lang.NullPointerException
at rekenmachine1.main(rekenmachine1.java:20)

Hi, I really wouldn't know how to fix the problem I'm experiencing, I hope you guys at Javaranch can help me.

What happens when I run the code: the JOptionPane dialog that lets the user choose the operation opens, I can enter the operation, then I click "ok" to go to the next box but my program closes after clicking "ok".

I've tried seeing what could be wrong in my code but I really can't spot what I did wrong.

import java.util.Scanner; import javax.swing.JFrame; import javax.swing.JOptionPane; public class rekenmachine1 { public static void main(String[] args) { JFrame frame = new JFrame("Calculator"); String operand; double num1; double num2; double total; String name = JOptionPane.showInputDialog(frame,"Choose a function: +, -, /, *" ); Scanner scan = new Scanner(System.in); operand = scan.next(); if (operand.equals("+")) { String option = JOptionPane.showInputDialog(frame,"Enter the first number of the sum" ); Scanner add1 = new Scanner(System.in); num1 = add1.nextDouble(); String option2 = JOptionPane.showInputDialog(frame,"Enter the second number of the sum" ); Scanner add2 = new Scanner(System.in); num2 = add2.nextDouble(); total = num1 + num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else if (operand.equals("-")) { String option = JOptionPane.showInputDialog(frame,"Enter the first number of the subtraction" ); Scanner sub1 = new Scanner(System.in); num1 = sub1.nextDouble(); String option2 = JOptionPane.showInputDialog(frame,"Enter the second number of the subtraction" ); Scanner sub2 = new Scanner(System.in); num2 = sub2.nextDouble(); total = num1 - num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else if(operand.equals("/")){ String option = JOptionPane.showInputDialog(frame,"Enter the number you wish to divide" ); Scanner div1 = new Scanner(System.in); num1 = div1.nextDouble(); String option2 = JOptionPane.showInputDialog(frame,"Enter the number you wish to divide the first number by" ); Scanner div2 = new Scanner(System.in); num2 = div2.nextDouble(); total = num1 / num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else if (operand.equals("*")) { String option = JOptionPane.showInputDialog(frame,"Enter the number you wish to multiply" ); Scanner mul1 = new Scanner(System.in); num1 = mul1.nextDouble(); String option2 = JOptionPane.showInputDialog(frame,"Enter the number you wish to multiply the first number by" ); Scanner mul2 = new Scanner(System.in); num2 = mul2.nextDouble(); total = num1 * num2; JOptionPane.showMessageDialog(frame, "The answer is: " + total); }else { JOptionPane.showMessageDialog(frame, "Oops, something went wrong, try again."); } } }


Thanks to anyone willing to take the time to help me out.