Java JFrame issue with dialog box

Question

When I run the program I'm facing some problem with JFrame Buffer, I don't know what the problem exactly is. When I run the program, it displays some dialog box part on the top left corner of the buffer.

Here is output of my program:

And following is the code

Thank you.

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

public class Main extends JPanel 
{
    public void paintComponent(Graphics g) 
    {
        super.paintComponent(g);
        int[] x1 = new int[10];
        int[] y1 = new int[10];
        int i,n;
        Polygon p=new Polygon();
        n = Integer.parseInt(JOptionPane.showInputDialog("Enter no. of co-ordinates of polygon: "));
        System.out.println(" no. of co-ordinates of polygon are :"+n);

        for(i=0;i<n;i++) 
        {  
            x1[i] = Integer.parseInt(JOptionPane.showInputDialog("Enter x co-ordinates of polygon: "));
            y1[i] = Integer.parseInt(JOptionPane.showInputDialog("Enter y co-ordinates of polygon: "));
        }
        for(i=0;i<n-1;i++)
        {
            g.drawLine(x1[i],y1[i],x1[i+1],y1[i+1]);
        }
        g.drawLine(x1[n-1],y1[n-1],x1[0],y1[0]);
    }

    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        frame.setTitle("Polygon");
        frame.setSize(500,500);
        Container contentPane = frame.getContentPane();
        contentPane.add(new Main());
        frame.setVisible(true);
    }
}

Answer 1

Never display an JOptionPane from a painting method. Painting methods are for painting only, they are not for getting user input.

Instead you need to do the following:

1. The JOptionPane should be displayed from the main method to gather the x/y parameters.

2. Modify your Main() class to have a method like addPoint(int x, int y).

3. The above method will then save the x/y values to an ArrayList object in your class. I would store Point objects in this list.

4. The painting method will then iterate through the List and then paint each line.