Question

I have Form on which i am drawing oval on mouseClick Event. This works Fine for me. The Circles are painted. But When i Minimize the Form and Again Maximize it the Panel gets Refreshed and Circles are removed (i.e Panel is left Blank).

Code is :
I have a JFrame on which there is a Jpanel named jPanel1, on this panel circles are drawn.

private void jPanel1MouseClicked(java.awt.event.MouseEvent evt) {
        count += 1;
        if (count <= clients) {
            drawCircle(evt.getX() - (radius / 2), evt.getY() - (radius / 2));
        }
    }

    public void drawCircle(int x, int y) {
        Graphics g = jPanel1.getGraphics();
        g.drawOval(x - radius, y - radius, 2 * radius, 2 * radius);
        g.setColor(Color.BLACK);
        g.fillOval(x - radius, y - radius, 2 * radius, 2 * radius);
    }

Answer 1

In this case, not only is it important to override your paintComponent method for the JPanel, but you also need to store the information about the circles you’re going to draw. You use that stored information to paint all the circles on the screen during the paintComponent call.

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;

import javax.swing.*;



public class TempProject extends JPanel{
    /** Stores info about circles  */
    public ArrayList<CircleInfo> circles = new ArrayList<CircleInfo>();

    /** fields that were in example code */
    public int count = 0;
    public final int radius = 20;
    public final int clients = 20;

    public TempProject(){

        addMouseListener(new MouseAdapter(){

            @Override
            public void mouseClicked(MouseEvent evt) {
                count += 1;
                if (count <= clients) {
                        // Store info about the circle to draw
                    circles.add(new CircleInfo(evt.getX() - (radius / 2), evt.getY() - (radius / 2), radius));
                        // Tell swing to repaint asap
                    repaint();
                }
            }});
    }

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

            //Iterates through saved circles and paints them
        for(CircleInfo circle : circles){
            g.drawOval(circle.x - circle.radius, circle.y - circle.radius, 2 * circle.radius, 2 * circle.radius);
            g.setColor(Color.BLACK);
            g.fillOval(circle.x - circle.radius, circle.y - circle.radius, 2 * circle.radius, 2 * circle.radius);
        }
    }

    public static void main(String args[])    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
                frame.setContentPane(new TempProject());  
                frame.setPreferredSize(new Dimension(400, 300));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    /** Simple class for storing Circle info */
    public static class CircleInfo{
        int x = 0;
        int y = 0;
        int radius = 0;

        public CircleInfo(int x, int y, int radius){
            this.x = x; this.y = y; this.radius = radius;
        }
    }

}