Qfyilyi

I tried making a very basic calculator, but if I try to output the calculated result I get the error that my variable "result" has not been initialised, even though I did initialise it inside the if-statement at the bottom. When I put the "System.out" line in my if-statement it works, so I have been wondering how can initialise a variable in my statement and keep the value.

But all I found were threads that talked about using "return" to give out a value, but not a variable.

import javax.swing.JOptionPane;

class Calculator{

public static void main(String args)

{

    double z1, z2, result;

    String input, s;



    input = JOptionPane.showInputDialog("Input a number:");



  //check whether or not the input is a number

        if(isNumber(input) == false)

        {

            JOptionPane.showMessageDialog(null, "Input a real Number", "Error",JOptionPane.ERROR_MESSAGE);

            System.exit(0);

        }



    z1 = Double.parseDouble(input);



    input = JOptionPane.showInputDialog("Input a second number:");



  //check whether or not the input is a number

        if(isNumber(input) == false)

        {

            JOptionPane.showMessageDialog(null, "Input a real number", "Error",JOptionPane.ERROR_MESSAGE);

            System.exit(0);

        }

    z2 = Double.parseDouble(input);



    s = JOptionPane.showInputDialog("Input an operation(+,-,*,/):");        



    if(s.equals("+"))

    { result = z1 + z2; }

    if(s.equals("-"))

    { result = z1 - z2; }

    if(s.equals("*"))

    { result = z1 * z2; }

    if(s.equals("/"))

    { result = z1 / z2; }



    System.out.println(result);

Since this code:

if(s.equals("+"))

{ result = z1 + z2; }

if(s.equals("-"))

{ result = z1 - z2; }

if(s.equals("*"))

{ result = z1 * z2; }

if(s.equals("/"))

{ result = z1 / z2; }

does not have a final else statement it is not guaranteed that result will be initialized.

One way to overcome this problem:

    if (s.equals("+")) {

        result = z1 + z2;

    } else if (s.equals("-")) {

        result = z1 - z2;

    } else if (s.equals("*")) {

        result = z1 * z2;

    } else if (s.equals("/")) {

        result = z1 / z2;

    } else {

        result = 0.0;

    }

or in the definition:

double result = 0.0;

The problem is that the environment checks whether everything is okay and sees that you have a few ifs where the variable might be initialized and finds that result is not guaranteed to be initialized. As a result you get this error. Try to initialize it at the start:

double z1, z2, result = 0;