如何将绘制的内容集中在JFrame中？

Question

I am trying to Center an oval drawn with JFrame & Color but I don't know how I would do this.

I know that I can get get the width by using Jframe#width() but I don't know how to do this in the method paintComponent , where I draw my circle. If I add a parameter to the Method, JFrame it doesn't work.

import javax.swing.*;
import java.awt.Graphics;
import java.awt.Color;
public class AU19b extends JPanel{
   protected void paintComponent(Graphics g){
        g.setColor(Color.RED);
        g.drawOval(10,10, 50, 50);
   }
    public static void main(String[] args){
        JFrame f = new JFrame("Sebastians GUI");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(400, 250);
        f.add(new AU19b());
        f.setVisible(true);
    }
}

Answer 1

use this to draw a circle with radius 50.

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

public class AU19b extends JPanel{

    @Override
    public void paintComponent(Graphics g){
        g.setColor(Color.RED);

        int radius = 50;

        g.drawOval(getWidth()/2 - radius,getHeight()/2 - radius, 2*radius, 2*radius);
    }
    public static void main(String[] args){
        JFrame f = new JFrame("Sebastians GUI");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(400, 250);
        f.add(new AU19b());
        f.setVisible(true);
    }
}