Unit 3: Java Programming

Chapter 5: GUI Development with Java Swing

1. What is Java Swing?

Java Swing is a lightweight, platform-independent Graphical User Interface (GUI) toolkit belonging to the Java Foundation Classes (JFC). - Located in the javax.swing.* package. - Replaced the older AWT (Abstract Window Toolkit) which was heavyweight and platform-dependent.

2. Core Swing Components and Properties

                            Component
                                |
                            Container
                                |
                 +--------------+--------------+
                 |                             |
               Window                       JComponent
                 |                             |
               JFrame         +----------------+----------------+
                              |                |                |
                            JPanel          JButton          JLabel
                                            JTextField       JCheckBox
                                            JTextArea        JRadioButton

Key Swing Controls Table

3. Event Handling in Java Swing

GUIs are event-driven. When a user interacts with a control (e.g., clicking a button), an Event is generated, transmitted to an Event Listener, and handled inside an Event Handler method.

The Delegation Event Model

1. Event Source: The GUI component generating the event (e.g., JButton).
2. Event Object: Encapsulates information about the event (e.g., ActionEvent).
3. Event Listener: An interface containing the callback handler method (e.g., ActionListener).

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

public class SimpleCalcGUI extends JFrame implements ActionListener {
    JTextField txt1, txt2;
    JLabel lblResult;
    JButton btnAdd;

    public SimpleCalcGUI() {
        setTitle("Quick Adder");
        setSize(300, 200);
        setLayout(null);

        txt1 = new JTextField();
        txt1.setBounds(50, 20, 100, 30);
        add(txt1);

        txt2 = new JTextField();
        txt2.setBounds(50, 60, 100, 30);
        add(txt2);

        btnAdd = new JButton("Add");
        btnAdd.setBounds(50, 100, 100, 30);
        btnAdd.addActionListener(this); // Register Listener
        add(btnAdd);

        lblResult = new JLabel("Result: 0");
        lblResult.setBounds(50, 140, 150, 30);
        add(lblResult);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    // Event Handler Method
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == btnAdd) {
            int a = Integer.parseInt(txt1.getText());
            int b = Integer.parseInt(txt2.getText());
            int sum = a + b;
            lblResult.setText("Result: " + sum);
        }
    }

    public static void main(String[] args) {
        new SimpleCalcGUI();
    }
}

4. Board Exam Focus & Practical Viva Questions

1. Why is ButtonGroup essential when using JRadioButton?
2. Ans: Without adding radio buttons to a ButtonGroup, each radio button acts independently and the user can check multiple buttons simultaneously, violating mutual exclusivity.
3. Which method is used to extract text entered into a JTextField?
4. Ans: getText() which returns a String. To convert to integer, use Integer.parseInt().
5. Differentiate between JTextField and JTextArea.
6. Ans: JTextField allows single-line text input, whereas JTextArea allows multi-line text input.