Java SE (Java Platform, Standard Edition)

Hi, I am new to Java.have looked in many topics of this forum, references and could not find the answer. thanks for helping.
I am trying to test a simple procedure to draw a line from (0,0) to (x,x), where x is an integer entered by the user using a showInputDialog.
I am using a JPanel and the paintComponent as suggested by some tutorial (so that, the frame can be moved, resized etc..and the line still remains there).

I have tried for hours how to get the x variable into the g.drawline method. Can anyone help.

Additionally, my frame has its top-left corner centered on the screen, resulting in the frame being shown in the bottom-right quadrant of the PC screen. How do I center it?

thanks for the help

package graphictest;

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class Draw extends JFrame {
    
     public Draw(){                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
        String inputString = JOptionPane.showInputDialogu(null,"enter input")l
        int input;
        input = Integer.parseInt(inputString);
        add(new NewPanel());
     } 
     
     public class NewPanel extends JPanel {
           protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawLine(0, 0,input, input);
            }
     }
 
    public static void main(String[] args) {   
        Draw frame = new Draw();
        frame.setTitle("Title");
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800,800); 
        frame.setVisible(true);
     }
}