Java Error Question

I wrote a crappy little calculator application for practice. When I go to compile the code, I get this exception returned:

Incompatible types:
Found: void
required java.lang.String

And then it points to a random place in the line of code that it says has an error. Here is the code:

Code:

---

import javax.swing.*;

public class JavaCalculator
{
        public static void main(String[] args)
        {
                //declare variables
                String choice;
                String inputOperation;
                String inputNumber1;
                String inputNumber2;
                String finalOutput;
                int number1;
                int number2;
               
                //get the operation from the user
                inputOperation = JOptionPane.showInputDialog(null, "Enter the type of operation you would like to perform.\n\n" + "Enter 'add', 'sub', 'mul', or 'div'. The field is not case sensitive.", "Java Calculator",  JOptionPane.PLAIN_MESSAGE);
               
                //check for operation type
                //perform operations accordingly
                if (inputOperation.equalsIgnoreCase("add"))
                {
                        //addition block
                        //get the numbers from the user
                        inputNumber1 = JOptionPane.showInputDialog(null, "Enter the first number: ", "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                        inputNumber2 = JOptionPane.showInputDialog(null, "Enter the second number: ", "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                       
                        //convert the numbers so that they are useable
                        number1 = Integer.parseInt(inputNumber1);
                        number2 = Integer.parseInt(inputNumber2);
                       
                        //output the final result
                        finalOutput = JOptionPane.showMessageDialog(null, "Your equation is: " + number1 + " + " + number2 + "\n" + "Your answer is: " + (number1 + number2), "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                }
                else if (inputOperation.equalsIgnoreCase("sub"))
                {
                        //subtraction block
                        //get the numbers from the user
                        inputNumber1 = JOptionPane.showInputDialog(null, "Enter the first number: ", "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                        inputNumber2 = JOptionPane.showInputDialog(null, "Enter the second number: ", "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                       
                        //convert the numbers so that they are useable
                        number1 = Integer.parseInt(inputNumber1);
                        number2 = Integer.parseInt(inputNumber2);
                       
                        //output the final result
                        finalOutput = JOptionPane.showMessageDialog(null, "Your equation is " + number1 + " - " + number2 + "\n" + "Your answer is: " + (number1 - number2), "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                }
                else if (inputOperation.equalsIgnoreCase("mul"))
                {
                        //multiplication block
                        //get the numbers from the user
                        inputNumber1 = JOptionPane.showInputDialog(null, "Enter the first number: ", "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                        inputNumber2 = JOptionPane.showInputDialog(null, "Enter the second number: ", "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                       
                        //convert the numbers so that they are useable
                        number1 = Integer.parseInt(inputNumber1);
                        number2 = Integer.parseInt(inputNumber2);
                       
                        //output the final result
                        finalOutput = JOptionPane.showMessageDialog(null, "Your equation is " + number1 + " * " + number2 + "\n" + "Your answer is " + (number1 * number2), "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                }
                else if (inputOperation.equalsIgnoreCase("div"))
                {
                        //division block
                        //get the numbers from the user
                        inputNumber1 = JOptionPane.showInputDialog(null, "Enter the first number: ", "Java Calculator",  JOptionPane.PLAIN_MESSAGE);
                        inputNumber2 = JOptionPane.showInputDialog(null, "Enter the second number: ", "Java Calculator",  JOptionPane.PLAIN_MESSAGE);
                       
                        //conver the numbers so that they are useable
                        number1 = Integer.parseInt(inputNumber1);
                        number2 = Integer.parseInt(inputNumber2);
                       
                        //output the final result
                        finalOutput = JOptionPane.showMessageDialog(null, "Your equation is " + number1 + " / " + number2 + "\n" + "Your answer is " + (number1 / number2), "Java Calculator", JOptionPane.PLAIN_MESSAGE);
                }
                System.exit(0);
        }
}

---

The exception is usually thrown around the message output for the answer. What is wrong here? I don't see anything.

Code:

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finalOutput = JOptionPane.showMessageDialog(null, "Your equation is " + number1 + " / " + number2 + "\n" + "Your answer is " +(number1 / number2), "Java Calculator", JOptionPane.PLAIN_MESSAGE);

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take out finalOutput since showMessageDIalog returns void.

and this applies to all 4 output :)

I didn't know that returned a void. Thx.