repainting my panel with objects

Question

I created a program that is supposed to draw a circle with each click(Random size and random color), and each circle is going to be an object. I don't know what is going on but my code doesn't work and I am pretty sure I am almost there.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Random;

public class Circle
{

    private JFrame frame;
    CircleObj circleObj;
    Random  rand;
    int rColor;
    int gColor;
    int bColor;
    int radius;



    public static void main (String [] arg)
        {

        frame = new JFrame("Circles");
        frame.setBounds(200, 100, 600, 480);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        JPanel top = new JPanel();
        rand = new Random();

        top.addMouseListener(new MouseAdapter()
        {
            public void mouseClicked(MouseEvent e)
                {
                int xstart = e.getX();
                int ystart = e.getY();
                rColor = rand.nextInt(256);
                gColor = rand.nextInt(256);
                bColor = rand.nextInt(256);
                radius = rand.nextInt(20);
                circleObj = new CircleObj(xstart, ystart, rColor, gColor, bColor, radius);

                repaint();

                }
        });
                frame.add(top, BorderLayout.CENTER);
                frame.setVisible(true);

        }


}

and here is my CircleObj class

import javax.swing.*;
import java.awt.*;

public class CircleObj extends JPanel

{
    private int xVal;
    private int yVal;
    private int red;
    private int green;
    private int blue;
    private int circleRadius;


    public CircleObj (int x, int y, int r, int g, int b, int rad)
        {
        xVal = x;
        yVal = y;
        red = r;
        green= g;
        blue = b;
        circleRadius = rad;

        }



        public void paintComponent (Graphics g) {
        super.paintComponent(g);
        g.setColor(new Color(red, green, blue));
        g.fillOval(xVal,yVal,circleRadius,circleRadius);
        }

}

Answer 1

Here is a second approach... How would I be able to tweak it store each circle in an object (Arraylist of objects) ?

public class Circle {
        public static void main (String[] arg) {
        JFrame frame = new JFrame("Circles");
        CircleObj canvas = new CircleObj();

        frame.add(canvas, BorderLayout.CENTER);
        frame.setBounds(250, 98, 600, 480);
        //frame.setLayout(new BorderLayout());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        } // end main
    } //end Circle

CircleObj Class

public class CircleObj extends JPanel {
    private int rColor;
    private int gColor;
    private int bColor;
    private int radius;
    private Random rand = new Random();
    private int xStart;
    private int yStart;

    public CircleObj () {
    addMouseListener(new MouseAdapter() {

        public void mouseClicked (MouseEvent e) {

        xStart = e.getX();
        yStart = e.getY();
        rColor = rand.nextInt(256);
        gColor = rand.nextInt(256);
        bColor = rand.nextInt(256);
        radius = rand.nextInt(20);
        System.out.println("xstart : " + xStart + ", ystart : " + yStart + ", rColor : " + rColor + ", gColor = " +
                gColor + ", bColor: " + bColor + ", radius: " + radius);

        repaint();
        }
    }); // end addMouseListener
    }

    public void paintComponent (Graphics g) {
    super.paintComponent(g);
    g.setColor(new Color(rColor, gColor, bColor));
    g.fillOval(xStart, yStart, radius, radius);
    }

}

Answer 2

You add a MouseListener to the top JPanel, but when do you add the top JPanel to the top-level window, the GUI? --- In the MouseListener! So this will never work since the top JPanel is not part of the GUI initially, and only gets added when a MouseListener that is added to it is triggered. The MouseListener only works on components that are visible and on the GUI.

Next you create a CircleObj object, but never draw with it in any JComponent's or JPanel's paiintComponent method.

I am pretty sure I am almost there.

So no, not quite. You will want to re-start and:

• Create a JPanel that has a decent paintComopnent method override,
• Add this JPanel to the JFrame to the GUI from the beginning.
• Add an ArrayList<CircleObj> to this drawing JPanel
• Change your CircleObj class so that it doesn't extend JPanel, but does have a public void draw(Grpahics g) method that will draw it.
• Add a MouseListener to the JPanel that controls this drawing. In your MouseListener, add a new CircleObj to the ArrayList and call repaint() to get the drawing JPanel to draw.
• In the JPanel's paintComponent override, iterate through the ArrayList<CircleObj> calling each object's draw(g) method.
• Read the Swing graphics tutorials.