// TEST CODES FOR CATCHING EXCEPTION (FRAME VERSION)

/* A simple applet that accepts a number and 
prints it at System.out. If no input is given, 
a JOption message is displayed. If the entry is 
non-numeric, a catch block catches the error and 
causes another JOption message to be displayed. */

/* To test the codes, compile this file using the 
command javac ExJFrame.java and run it using the 
command java ExJFrame. */

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ExJFrame extends JFrame implements ActionListener
{

   JPanel panel;
   JLabel labQty;
   JTextField txtQty;
   JButton btnOk;
   GridBagLayout gbl;
   GridBagConstraints gbc;

   public ExJFrame() // Buid the panel and add to frame
   {
      panel= new JPanel();
      labQty = new JLabel("Qty");
      txtQty = new JTextField(5);
      btnOk = new JButton("OK");
      gbl = new GridBagLayout();
      gbc = new GridBagConstraints();
      panel.setLayout(gbl);
      getContentPane().add(panel);
      gbc.anchor = GridBagConstraints.NORTHWEST;

      gbc.gridx = 0;
      gbc.gridy = 0;
      gbl.setConstraints(labQty, gbc);
      panel.add(labQty);

      gbc.gridx = 1;
      gbc.gridy = 0;
      gbl.setConstraints(txtQty, gbc);
      panel.add(txtQty);

      gbc.gridx = 1;
      gbc.gridy = 1;
      gbl.setConstraints(btnOk, gbc);
      panel.add(btnOk);
      btnOk.addActionListener(this);
   }

   public void checkQty() // Check what value we got
   {
      int num;
      String tmp = txtQty.getText();
      if(tmp.length() == 0) // Is Qty empty?
      {
         JOptionPane.showMessageDialog( null, "Qty should not be empty.", "Opps", JOptionPane.ERROR_MESSAGE );
      }
      else
      {
         try
         {
            num = Integer.parseInt(tmp);
            System.out.println("\nQty is " + num);
         }
         catch(NumberFormatException x)
         {
            JOptionPane.showMessageDialog( null, "Qty should be numeric.", "Opps", JOptionPane.ERROR_MESSAGE );
         }
      }
   }
      
   public void actionPerformed(ActionEvent e) // OK button listener
   {
      if(e.getSource() == btnOk)
      {
         checkQty();
      }
   }

   public static void main(String args[])
   {
      ExJFrame ef = new ExJFrame();
      ef.setSize( 200, 200 );
      ef.addWindowListener(new WindowAdapter()
      {
         public void windowClosing(WindowEvent we) // Exit on Close
         {
            System.exit(0);
         }
      });
      ef.setVisible( true );
   }
}

/* Modify the code so that a message dialog 
containing the message Command Successful is 
displayed if the user entered integer numbers 
in the Quantity field. */