What's Wrong with this JFrame??? I can't see the label.

Question

I was making a simple JFrame window and I was previewing my work but I couldn't see the label I put in it. It shows a window but no text from the label or red background.
Thanks.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class FirstClass extends JFrame{
     final static long serialVersionUID = 0;
     public FirstClass(){
          this.setSize(new Dimension(600,300));
          this.setVisible(true);
          Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
          Dimension frameSize = this.getSize();
          int x = (screenSize.width/2) - (frameSize.width/2);
          int y = (screenSize.height/2) - (frameSize.height/2);
          this.setLocation(x,y);
          this.addWindowListener( new WindowAdapter(){
               public void windowClosing(WindowEvent e){
                    System.exit(0);
          JPanel p = new JPanel();
          p.setBackground(Color.RED);
          p.setLayout(new BorderLayout());
          getContentPane().add(p);
          Label l = new Label();
          l.setText("Hello World");
          p.add(l);
     public static void main(String[] args) {
          FirstClass fc = new FirstClass();
          fc.setTitle("Test");
}

Answer 1

your sequence for setVisible() is incorrect.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class FirstClass extends JFrame{
     final static long serialVersionUID = 0;
     public FirstClass(){
          this.setSize(new Dimension(600,300));
          //this.setVisible(true); //remark this line
          Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
          Dimension frameSize = this.getSize();
          int x = (screenSize.width/2) - (frameSize.width/2);
          int y = (screenSize.height/2) - (frameSize.height/2);
          this.setLocation(x,y);
          this.addWindowListener( new WindowAdapter(){
               public void windowClosing(WindowEvent e){
                    System.exit(0);
          JPanel p = new JPanel();
          p.setBackground(Color.RED);
          p.setLayout(new BorderLayout());
          getContentPane().add(p);
          Label l = new Label();
          l.setText("Hello World");
          p.add(l);
          this.setVisible(true); //add this line
     public static void main(String[] args) {
          FirstClass fc = new FirstClass();
          fc.setTitle("Test");
}