Help please- GUI calculator

Question

I am trying to create a GUI calculator which:
-must use the JOptionPane class to create dialog boxes for user input and
output.
-If the user attempts to divide by 0, you must print a message to that effect (e.g.,
"division by 0 not allowed").
-If the user enters an invalid operator, you must print a message to that effect
(e.g., "operation not supported").
My Program will not work, and any help would be greatly appreciated!
import javax.swing.JOptionPane;
public class GUI {
     String numberString =
          JOptionPane.showInputDialog("Welcome to my GUI Calculator!\n The following operations are supported:\n +(addition), -(subtraction), *(multiplication)\n /(division),and ^(exponent)\n\n Enter your calculation separated by spaces and press OK.\n Example:2.5 + 3");
     int firstSpace =
     numberString.indexOf(" ");
     double answer;
     double
     operand1 = Double.parseDouble(numberString.substring(0,firstSpace));
     double
     operand2 = Double.parseDouble(numberString.substring(firstSpace+3,numberString.length()));
     char
     operator = numberString.charAt(firstSpace+1);
     while (operator == "+")
          answer = operand1 + operand2;
     while (operator == "-")
          answer = operand1 - operand2;
     while (operator == "*")
          answer = operand1 * operand2;
     while (operator == "/")
     { if (operand2 == 0)
          JOptionPane.showInputDialog("Division by 0 not allowed!");
          else
          answer = operand1 / operand2;
     while (operator == "^")
          answer = Math.pow(operand1, operand2);
while (operator != "+, -, *, /, ^")
     JOptionPane.showInputDialog("Operation not supported.");
JOptionPane.showMessageDialog("numberString = answer");
System.exit(0);
}

Answer 1

When you post code, please wrap it in [code] [/code] tags so it's easy to read.
You're confusing strings with characters. You read the operator as a character. But when you check it, you compare it with Strings (you can tell they're Strings because you're using double quotes). You should be using single quotes there.
Your code makes a lot of assumptions about the format of the data it's given, for example the number of spaces and where they'll appear.
And this part:while (operator != "+, -, *, /, ^") There's absolutely no reason why that would work. Where did you get the idea that was a thing to do? If you want to see if the operator is in a list of characters, there are a variety of things you can do, but probably the simplest is just to have five if/else statements. You're going to need those anyway when you do the math operation; when you get to the last one, just put an else statement saying that you don't recognize the operator.