import javax.swing.*; // swing is a library of GUI components 

// example of using message boxes to get input and show output
public class GUI_IO {

	// use input dialog to get user input
	public static int getInt(String msg) {
		boolean first = true;
    boolean done = false;
		// keep trying until we get a valid int
		// (loop actually ends when we return the number at the end of try)
		while (!done) {
			try {
				// showInputDialog returns a string
				// which we then try to parse as int to get our result
				// if user input not an int, exception is thrown
				String user = JOptionPane.showInputDialog(msg);
				int value = Integer.parseInt( user );
			  done = true;
				return value;				
				// often we'd do this all in one line:
				//return Integer.parseInt( JOptionPane.showInputDialog(msg) );
			
			} catch(NumberFormatException e) {
				// add nasty note after first bad input
				if (first) {
					msg = "Invalid, please enter an integer.\n" + msg;
					first = false;
				}
			}
		}
	}

	// get two ints and show a message with the sum.
	public static void main(String[] args) {
		// short version of message dialog
		JOptionPane.showMessageDialog(null, "WELCOME");
		
		// calling method above to get input
		int n1 = getInt("What is the first number?");
		int n2 = getInt("What is the second number?");
		
		// long version of message dialog
		JOptionPane.showMessageDialog(
			null, 									// parent window to center over -- none here
			n1 + " + " + n2 + " = " + (n1 + n2), 	// output to show
			"Result", 								// message box title
			JOptionPane.INFORMATION_MESSAGE);		// message box style  
													// PLAIN_MESSAGE, INFORMATION_MESSAGE, ERROR_MESSAGE, WARNING_MESSAGE, QUESTION_MESSAGE
	}
}