What is the reason for the output not appearing when running the code and what is the necessary modification to it?

package components;
import java.awt.FlowLayout;
import javax. swing. JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
public class Components extends JFrame {
    private JTextField tf1,tf2,tf3;
    private JLabel b1;
     private JComboBox comb1, comb2;
      public Components () {
          this.setSize (500,500);
          this. setLocationRelativeTo (null);
          this.setResizable (false);
          this.setVisible (true);
          this.setLayout (new FlowLayout ());
           b1= new JLabel ("Enter you Student Number:");
           tf1= new JTextField("Student Number");
           tf2= new JTextField(40);
           String [] items= {"book1","book2", "book3"};
           comb2 = new JComboBox(items) ;
           comb1 = new JComboBox();
           add(b1); add(tf1); add(tf2);add(tf3) ;add(comb1) ;add(comb2);
    public static void main(String[] args) {
        Components c= new Components();

Would you mind sending a screenshot of what your repl currently shows?