Does invoking the drawRect method on a Graphics2D trigger the paintComponent method?

Question

I'm trying to figure out the behavior of my program, and that is my best theory as to why its doing what its doing. I was hoping this would use the rand variable to decide which shape to paint, but instead it seems the paintComponent method is being invoked many times in-between timer firings, causing many shapes to be painted and I'm trying to understand why.

This is the code:

public class TestPane extends JPanel {

    private int yPos0;
    private int yPos1;
    private int boundary0=750;
    private ActionEvent ae = null;
    private Graphics g0 = null;
    private int count=1;

    public TestPane(Color foreground){
        setForeground(foreground);
        this.setBackground(Color.BLUE);
        Timer timer = new Timer(3000,new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e){
                ae = e;
                 yPos0 =yPos0+50;
                    repaint();
            }
        });
        timer.start();
    }

    @Override
    public void paintComponent(Graphics g){
             g0 = g;
             super.paintComponent(g);
             createShape(yPos0);
             repaint(); 
    }

    public void createShape(int ypos0){
        //generate random number between 1 and 3 and assign to rand
        int rand = (int)((Math.random()*3)+1);

        System.out.println(rand);
        if(rand==1){
            Graphics2D g2d = (Graphics2D) g0.create();
            g2d.setColor(Color.RED);
            g2d.drawRect(0, ypos0, 200, 50);
        }

        if(rand==2){
            Graphics2D g2d = (Graphics2D) g0.create();
            g2d.setColor(Color.GREEN);
            g2d.drawRect(0, ypos0, 150, 50);
            g2d.drawRect(50, ypos0+50,50,50);
        }
    }
}

Answer 1

The reason that paintComponent is being called so many times is that you are calling repaint within that method which causes itself to be called ad infinitum . This is not needed as you're already calling repaint from your Timer .