Plotting random points in Java using 2D Graphics

Question

I am beginner to java Graphics , I have been trying to plot random dots on JFrame but don't know why when I compile there is nothing on Frame , for me logic is fine + no error. Can someone help me whats wrong here

public class parent extends JPanel {    

    public void PaintComponent (Graphics g)     
    {
        super.paintComponent(g);
        Graphics2D g2d  = (Graphics2D) g;
        g2d.setColor(Color.blue);
        Dimension size = getSize();
        Insets  insets= getInsets();
        int w =  size.width - insets.left - insets.right;
        int h =  size.height - insets.top - insets.bottom;
        Random r = new Random();

        for (int i=0; i<1000; i++) {
           int x = Math.abs(r.nextInt()) % w;
           int y = Math.abs(r.nextInt()) % h;
           g2d.drawLine(x, y, x, y);
        }
    }


    public static void main(String[] args) 
    {
        JFrame frame = new JFrame("Points");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new parent());
        frame.setSize(250, 200);
        frame.setVisible(true);
     }
} 

Answer 1

Well is it PaintComponent or should it be paintComponent ? I think I know which one the Java developers would choose.

Note that this is a perfect bug that @Override in annotation would catch in Eclipse.

Answer 2

From your code, you are using the DrawLine to draw from (x, y) to (x, y). Which would be a single pixel. And you have set the Color Blue. Therefore it will not be very visible, regardless of the color.

But aside from that, your loop calculates the X and Y values based upon the Random Number R, and yet R is never re-calculated as a new Random Number (you set it once before the loop, and never reset it). So that will then re-plot the same point over-and-over again 1,000 times.

If you put the Random Number Calculation inside the loop, and have it draw a circle with a radius of, oh, 5-10 pixels, around your random point, it will be much more visible. And then you should be on the way to accomplishing your goal.