JFrame window dimensions

package temporary;

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

public class Temp extends JFrame {
     Graphics2D painter2D;
     static int W = 1200;
     static int H = 600;
     static int B = 10; // border

     public Temp() {
         super("Temp");
         setSize(W + 8, H + 36); // necessary adjustment
         System.out.println("1 " + getWidth() + " " + getHeight());
         // 1 1208 636
         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         setVisible(true);
         Container contentArea = getContentPane();
         CustomPanel panel = new CustomPanel();
         contentArea.add(panel);
         setContentPane(contentArea);
     }

     public static void main(String[] args) {
         Temp instance = new Temp();
     }

     class CustomPanel extends JPanel {
         public void paintComponent(Graphics painter) {
             System.out.println("2 " + getWidth() + " " + getHeight());
             // 2 1200 600
             painter2D = (Graphics2D) painter;
             painter2D.translate(0, H / 2); // middle horizontal 0

             // draw the frame
             Color clr = Color.black;
             drawFrame(clr);
         }

         private void drawFrame(Color clr) {
             double x, y, w, h;
             x = 0 + B;
             y = -H / 2 + B;
             w = W - 2 * B;
             h = H - 2 * B;
             Rectangle2D.Double frame = new Rectangle2D.Double(x,y,w,h);
             painter2D.setColor(clr);
             painter2D.fill(frame);
         }
     }
}

In the above program, I want the active window (that is the area I am
working in, without the top bar and the borders) to be 1200 by 600. To
do so, I had to use

     setSize(W + 8, H + 36);

to compensate for the width and height of the top bar and borders I have
in my system. If I do not make this adjustments, the frame will be
off-center. I found them empirically, by using

     System.out.println("2 " + getWidth() + " " + getHeight());

within the

     public void paintComponent(Graphics painter) {

Is there a way to get the necessary adjustment values of the system
automatically instead of empirically? Is there a way to reset the size
after I know the values of the adjustments in the
paintComponent(Graphics painter)?

Thanks,

emf

--
It ain't THAT, babe! - A radical reinterpretation
https://files.nyu.edu/emf202/public/bd/itaintmebabe.html