Phase 7: GUI Programming (AWT & Swing)

Java provides AWT (Abstract Window Toolkit) and Swing for desktop GUI development. Learn the heavyweight vs lightweight distinction and layout management.

1. AWT vs Swing (Crucial Comparison)

Feature	AWT (Abstract Window Toolkit)	Swing (Java Foundation Classes)
Component Type	Heavyweight (uses native OS peer components).	Lightweight (written purely in 100% Java).
Platform Dependence	Platform dependent (looks like native Windows/Mac OS).	Platform independent (Pluggable Look and Feel - PLAF).
Speed & Memory	Faster execution, higher OS resource consumption.	Slightly slower execution, richer component library.
Package Name	`java.awt.*` (e.g., `Button`, `Frame`)	`javax.swing.*` (e.g., `JButton`, `JFrame`)

2. Layout Managers

Layout managers automatically position and size GUI components inside a Container:

FlowLayout: Default for JPanel. Arranges components left-to-right, top-to-bottom.
BorderLayout: Default for JFrame. Divides container into 5 regions: NORTH, SOUTH, EAST, WEST, and CENTER.
GridLayout: Arranges components in a fixed rectangular grid of equal-sized rows and columns.
GridBagLayout: The most flexible and complex layout manager; components span multiple rows/columns using constraints.

3. Event Delegation Model

[Event Source (e.g. JButton)] ──(generates ActionEvent)──► [Event Listener (ActionListener)]
                                                                  │
                                                        executes actionPerformed()
        

To handle a button click in Swing:

JButton btn = new JButton("Submit");
btn.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("Button Clicked!");
    }
});
        

⚡ Quick Self-Test

Q: What is the default layout manager for a Swing JFrame?

Answer: BorderLayout.
A JFrame defaults to BorderLayout, whereas a JPanel defaults to FlowLayout.