Question

I am trying to draw graphics based on a button click using boolean flags. Before, I set the boolean value as a public static boolean type in the ShapeGUI class, and called it in ShapeListener using Shape.draw and that worked, although it took around 10 seconds to conjure a drawing.

Now I set the boolean flag inside the ShapeListener class itself. Now its either not repainting or is very slow. How can I make a drawing appear instantly when I click a button?

public class ShapeGUI extends JFrame
{
    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;

    public ShapeGUI()
    {
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //setLayout(new FlowLayout());
        setLocationRelativeTo(null);
        JMenuBar menu = new JMenuBar();
        JMenu file = new JMenu("File");
        menu.add(file);
        JMenuItem save = new JMenuItem("Save Information");
        JMenuItem exit = new JMenuItem("Exit");
        file.add(save);
        file.add(exit);               
        setJMenuBar(menu);

        ShapeListener test = new ShapeListener();        
        JButton button = new JButton("Hello"); 
        test.setBackground(Color.CYAN);
        button.addActionListener(new ShapeListener());
        test.add(button); 
        add(test);

//followed this person's advice        
//First off, your drawing should be done in a paintComponent method override that is held in a class that extends JPanel. Next, this class could have a boolean variable that the paintComponent uses to decide if it will draw a rectangle or not. The button press simply sets the boolean variable and calls repaint on the drawing JPanel.
    }
}

    public class ShapeListener extends JPanel implements ActionListener

    {

    boolean draw = false;
    Shape s = new Circle();
    Shape a = new Rectangle();

    @Override
    public void actionPerformed(ActionEvent e) 
    {
        draw = true;
        repaint();
    }
    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        if(draw)
        {
        s.draw(g);
        }
        else
        {
            a.draw(g);
        }

    }

}

Answer 1

Your logic is a little off…

ShapeListener test = new ShapeListener(); // First instance
JButton button = new JButton("Hello");
test.setBackground(Color.CYAN);
button.addActionListener(new ShapeListener()); // Second instance...
test.add(button);
add(test);

You create two instance of the ShapeListener class, add one to the container and use the other as the action listener. Neither will know about each other, meaning that you can click to the cows come home, the first instance of ShapeListener will never change.

Also, unless you’re planning to override the preferredSize method of the ShapeListener pane, I’d use something like a BorderLayout on the frame, to ensure that the panel is properly laid out, otherwise it will look like the panel isn’t being painted…

Try something like…

public class ShapeGUI extends JFrame {

    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;

    public ShapeGUI() {
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        JMenuBar menu = new JMenuBar();
        JMenu file = new JMenu("File");
        menu.add(file);
        JMenuItem save = new JMenuItem("Save Information");
        JMenuItem exit = new JMenuItem("Exit");
        file.add(save);
        file.add(exit);
        setJMenuBar(menu);

        setLayout(new BorderLayout());

        ShapeListener test = new ShapeListener();
        JButton button = new JButton("Hello");
        test.setBackground(Color.CYAN);
        button.addActionListener(test);
        test.add(button);
        add(test);

        setVisible(true);

    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                new ShapeGUI();

            }
        });
    }

    public class ShapeListener extends JPanel implements ActionListener {

        Shape s = new Ellipse2D.Float(0, 0, 20, 20);
        Shape a = new Rectangle2D.Float(0, 0, 20, 20);

        private Shape paintMe = a;

        @Override
        public void actionPerformed(ActionEvent e) {
            paintMe = s;
            repaint();
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);

            int x = (getWidth() - paintMe.getBounds().width) / 2;
            int y = (getHeight() - paintMe.getBounds().height) / 2;

            Graphics2D g2d = (Graphics2D) g.create();
            g2d.translate(x, y);
            g2d.draw(paintMe);
            g2d.dispose();

        }
    }
}

instead…