Java GUI 填充图形怎么放大和缩小

 public class myJFrame extends JFrame implements ActionListener {
    private JButton but1, but2, but;
    Container cp = this.getContentPane();
    JPanel p = new JPanel(new FlowLayout(1, 5, 5));

    public myJFrame() {
        super("彭杰的窗口");
        but1 = new JButton("放大");
        but2 = new JButton("缩小");
        but1.addActionListener(this);
        but2.addActionListener(this);
        p.add(but1);
        p.add(but2);
        cp.add(p, BorderLayout.SOUTH);
    }

    public void paint(Graphics g) {
        super.paint(g);
        g.setColor(Color.green);
        g.fillOval(150, 150, 100, 100);
    }

    public void actionPerformed(ActionEvent e) {
        JButton but = new JButton();
        but = (JButton) e.getSource();
        if (but1 == but) {
            System.out.println("你点击了放大");
        }
        if (but2 == but) {
            System.out.println("你点击了缩小");
        }

    }
}

图片没放大，就做了个点击事件的监听器？