Hello,

The following program computes the value of Pi using the Hit/Miss method. Since I am doing all the drawing in the JPanel, I am not calling super.paintComponent(g). The program works well, but since I am not using the super.paintComponent, it does not draw the background. Is there any way to draw the background without using super.paintComponent(g)?

Thank you!

        import java.awt.Color;
        import java.awt.Graphics;
        import java.awt.Graphics2D;
        import java.awt.geom.Line2D;
        import java.util.Scanner;
        import java.awt.event.*;
        import javax.swing.*;
        import javax.swing.JFrame;
        import javax.swing.JPanel;
        import java.awt.image.BufferedImage;


        public class estimatingPi extends JPanel implements Runnable
        {
            static int side, trials;
            int countOut = 0, count = 0, countIn = 0;
            private static BufferedImage image;
            boolean flag = true;
            private Thread thread;
            private Graphics g;

            public static void main(String args[])
            {
                Scanner s = new Scanner(System.in);

                System.out.println("Monte Carlo - Estimating Pi\n---------------------------\n\nInput the size of the sides of the square");
                side = s.nextInt();

                System.out.println("Input the number of trials");
                trials = s.nextInt();



                estimatingPi pi = new estimatingPi();
                JFrame p = new JFrame ("Hit and Miss - Estimating Pi");
                p.add(pi);
                p.setSize(500, 500);
                p.setVisible(true);    


            }

            public estimatingPi()
            {
                setBackground (Color.BLACK);
                thread = new Thread (this);
                thread.start();
            }

            public boolean checkPosition(double x, double y)
            {
                double cen = side/2;

                if(Math.sqrt(Math.pow(cen-x, 2) + Math.pow(cen-y, 2)) > side/2)
                    return true;
                else 
                    return false;
            }

            public void paintComponent(Graphics g) 
            {

                  Graphics2D g2 = (Graphics2D) g;
                  g2.setColor(Color.CYAN);
                  g2.drawOval(0, 0, side, side);
                  g2.setColor(Color.RED);
                  g2.drawLine(0, side, side, side);
                  g2.drawLine(side, side, side, 0);


                   boolean in;
                   double x = Math.random() * side;
                   double y = Math.random() * side;

                    if(checkPosition(x, y))
                      {
                          g2.setColor(Color.RED);                 
                          Line2D.Double l = new Line2D.Double(x, y, x, y);
                          g2.draw(l);
                          countOut++;
                      }
                      else
                      {
                          g2.setColor(Color.BLUE);
                          Line2D.Double l = new Line2D.Double(x, y, x, y);
                          g2.draw(l);
                          countIn++;
                      }
                      count++;

             }   

            public void run()
            {
                while (flag == true)
                 {
                      try
                            {
                                thread.sleep(10);
                            }
                      catch (InterruptedException e)
                         {}

                      if (count == trials)
                      {
                        System.out.println("Out: " + countOut + "\nIn: " + countIn);
                        double piEstimated = 4*((double)countIn/(double)trials);
                        System.out.println("Pi is estimated to be: " + piEstimated);
                        flag = false;
                      }
                      repaint();

                }
            }
        }

Edited 4 Years Ago by javaprog200

Hello,

Thank you for the reply!

fillRect() inside the paintComponent() makes the dots invisible. fillRect inside the constructor (written below) gives me a NullPointerException():

 public estimatingPi()
        {
            thread = new Thread (this);
            thread.start();
            getGraphics().setColor (Color.BLACK);
            getGraphics().fillRect (0, 0, 500, 500);
        }

What I am doing wrong?

Please explain when you want the color to be set for the background.
If only one time at the start, use a boolean variable in the paintComponent method to control the calling of fillRect() just one time.

Edited 4 Years Ago by NormR1

Hello,

Yes - I only want the background to be colored once at the start. Hence, I tried as suggested by you. I am not able to get the background to be black. Please let me know what I am doing wrong.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Line2D;
import java.util.Scanner;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.image.BufferedImage;


public class estimatingPi extends JPanel implements Runnable
{
    static int side, trials;
    int countOut = 0, count = 0, countIn = 0;
    private static BufferedImage image;
    boolean flag = true, flag1 = true;
    private Thread thread;
    private Graphics g;

    public static void main(String args[])
    {
        Scanner s = new Scanner(System.in);

        System.out.println("Monte Carlo - Estimating Pi\n---------------------------\n\nInput the size of the sides of the square");
        side = s.nextInt();

        System.out.println("Input the number of trials");
        trials = s.nextInt();



        estimatingPi pi = new estimatingPi();

        JFrame p = new JFrame ("Hit and Miss - Estimating Pi");
        p.add(pi);
        p.setSize(500, 500);
        p.setVisible(true);    


    }

    public estimatingPi()
    {
        thread = new Thread (this);
        thread.start();

    }

    public boolean checkPosition(double x, double y)
    {
        double cen = side/2;

        if(Math.sqrt(Math.pow(cen-x, 2) + Math.pow(cen-y, 2)) > side/2)
            return true;
        else 
            return false;
    }

    public void paintComponent(Graphics g) 
    {

          Graphics2D g2 = (Graphics2D) g;
          g2.setColor(Color.CYAN);
          g2.drawOval(0, 0, side, side);
          g2.setColor(Color.RED);
          g2.drawLine(0, side, side, side);
          g2.drawLine(side, side, side, 0);

          if (flag1 == true)
              {
                  g2.setColor (Color.BLACK);
                  g2.fillRect (0, 0, 500, 500);
                  flag1 = false;
              }

           boolean in;
           double x = Math.random() * side;
           double y = Math.random() * side;

            if(checkPosition(x, y))
              {
                  g2.setColor(Color.RED);                 
                  Line2D.Double l = new Line2D.Double(x, y, x, y);
                  g2.draw(l);
                  countOut++;
              }
              else
              {
                  g2.setColor(Color.BLUE);
                  Line2D.Double l = new Line2D.Double(x, y, x, y);
                  g2.draw(l);
                  countIn++;
              }
              count++;

     }   

    public void run()
    {
        while (flag == true)
         {
              try
                    {
                        thread.sleep(10);
                    }
              catch (InterruptedException e)
                 {}

              if (count == trials)
              {
                System.out.println("Out: " + countOut + "\nIn: " + countIn);
                double piEstimated = 4*((double)countIn/(double)trials);
                System.out.println("Pi is estimated to be: " + piEstimated);
                flag = false;
              }
              repaint();

        }
    }
}
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