Event Handling: Listeners

The Delegation Model

AWT uses the delegation event model: a component fires events and registered listeners react. Register a listener with addXxxListener(...).

Button Action

btn.addActionListener(e -> status.setText("Clicked!"));

Mouse Events

Implement MouseListener or extend MouseAdapter:

canvas.addMouseListener(new MouseAdapter() {
    public void mouseClicked(MouseEvent e) {
        info.setText("Clicked at " + e.getX() + "," + e.getY());
    }
});

Keyboard Events

Implement KeyListener to react to key presses:

field.addKeyListener(new KeyAdapter() {
    public void keyTyped(KeyEvent e) {
        System.out.println("Typed: " + e.getKeyChar());
    }
});

Key Points

• Adapters (MouseAdapter, KeyAdapter) let you override only the methods you need.
• ActionListener is for buttons, text fields and menu items.
• Event objects carry details like coordinates and key codes.