Question

1. display a dialog box which contains the message "Input a value for size (>0)";
2. assume the input is a number, check if it is less than or equal to zero. If so, display the message "Size must be > 0" in another dialog box and go to 1;

I got trouble in question 2. After I display the message of "Size must be >0", how can I repeat the step in question 1 and make it like a looping?

//The class to model the class Orange
//Import statement for resolving the class JOptionPane
import javax.swing.*;

//The class definition of TestOrange
public class TestOrange {
  
//The main executive method
public static void main (String[] args) {
Orange orangeA;
orangeA = new Orange();
  
//Print the message "An object orangeA of class Orange"
System.out.println("An object orangeA of class Orange has been created");
  
//Show a dialog for getting the size of orange
String inputSize = JOptionPane.showInputDialog("Input a value for size (>0)");

//Obtain the double value from the input String object
double size = Double.parseDouble (inputSize);
  
//Show message dialog if size is less than or equal to zero
if(size<=0) {
String output = "Size must be >0";
JOptionPane.showMessageDialog(null,output);
}

//Print the category of the orange if size is greater 0
else {
orangeA.setSize(size);
System.out.println(orangeA.category());
}
}   
}

Answer 1

thanks for the question, here is the how you need to loop until user enters a positive number. I have commented the additional lines so that you can follow it.

thanks : )

=========================================================================================

import javax.swing.*;

//The class definition of TestOrange
public class TestOrange {

    //The main executive method
    public static void main(String[] args) {
        Orange orangeA;
        orangeA = new Orange();

//Print the message "An object orangeA of class Orange"
        System.out.println("An object orangeA of class Orange has been created");


        // infinite while loop until user enters a size > 0
        while (true) {
            //Show a dialog for getting the size of orange
            String inputSize = JOptionPane.showInputDialog("Input a value for size (>0)");
            //Obtain the double value from the input String object
            double size = Double.parseDouble(inputSize);

            //Show message dialog if size is less than or equal to zero
            if (size <= 0) {
                String output = "Size must be >0";
// JOptionPane.showMessageDialog(null, output); // this line is not needed any more
            }
            //Print the category of the orange if size is greater 0
            else {
                orangeA.setSize(size);
                System.out.println(orangeA.category());
                // when the size is greater than 0 we break out of while loop using break statement
                break;

            }
        }

    }
}