Illustrate the method to print on the GUI

Example Code: Taking Input / Output

So far, we learned how to print something on console. Now time has come to learn how to print on the GUI. Taking input from console isn't as straightforward as in C++. At first we'll study how to take input through GUI (by employing JOPtionPane class).

The following program will take input (a number) through GUI and prints its square on the console as well on

GUI.

1. import javax.swing.*;

2. public class InputOutputTest {

3. public static void main(String[] args) {

4. //takes input through GUI

5. String input = JOptionPane.showInputDialog("Enter number");

6. int number = Integer.parseInt(input);

7. int square = number * number;

8. //Display square on console

9. System.out.println("square:" + square);

10. //Display square on GUI

11. JOptionPane.showMessageDialog(null, "square:"+ square);

12. System.exit(0);

13. }

14. }

On line 1, swing package was imported since it comprise JOptionPane class which will be used for taking input from GUI and displaying output to GUI. It's similar to header classes of C++.

On line 5, showInputDialog method is called of JOptionPane class by passing string argument which would be displayed on GUI (dialog box). This method always returns back a String regardless of whatever you entered (int, float, double, char) in input filed.

Our task is to print square of a number on console thus we first convert a string into a number by calling parseInt method of Integer wrapper class. This is what we done on line number 6.

Line 11 would display square on GUI (dialog box) by using showMessageDialog method of JOptionPane class. First argument passed to this method is null and second argument should be a String. Here we use string concatenation.

Line 12 is required to return control back to command prompt whenever we use JoptionPane class.