扩展JFrame时，JPanel无法正确显示

Question

This is my homework.

My directions: Class GuessGame: This class contains the main function which creates a JFrame object, sets up the JFrame's size, visibility and exit.

Class GuessGameFrame: GuessGameFrame class extends JFrame. So the GuessGameFrame class has all variables and methods defined in class JFrame.

I am not 100% sure what my problem is but I believe the JPanel is not working correctly

Any help would greatly be appreciated, if I left out anything important please let me know and I can add more detail.

main class:

public class GuessGame {

             public static void main(String[] args){
                  GuessGameFrame localGuessGameFrame = new GuessGameFrame();
                  localGuessGameFrame.setVisible(true); //set visible
                  localGuessGameFrame.setSize(380,175); // set size 380 width 175 height
                  localGuessGameFrame.setDefaultCloseOperation(localGuessGameFrame.EXIT_ON_CLOSE); // needed to enable the red X button to close the program
             }
}

extended class:

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

public class GuessGameFrame extends JFrame
    {

    private int lastDistance; // distance between last guess and number
    private Color background; // background color of application

    private JFrame f;
    static JPanel p;
    private JButton b1;
    private JLabel l1;
    private JLabel l2;
    JTextField t1 = new JTextField(8);
    private JLabel l3;

    //declare constructor
    public GuessGameFrame()
    {
    //create our JFrame
    f = new JFrame("Guessing game");

    //create our panel
        p = new JPanel();
        p.setBackground(Color.MAGENTA); // background color is magenta

        //create our labels
        l1 = new JLabel("I have a number between 1 and 1000.");
        l2 = new JLabel("Can you guess my number? Enter your first Guess:.");
        l3 = new JLabel("Guess result appears here.");
        //create our button
        b1 = new JButton("New Game");

        //add button and label to panel
        p.add(l1); // Adds label 1
        p.add(l2); // adds label 2
        p.add(t1); // adds textfield 1
        p.add(l3); // adds label 3
        p.add(b1); // adds button 1

        //add panel to JFrame
        f.add(p);
    }
}

Screenshot of the output window when executed:

I expect it to look like this:

Answer 1

You need remove JFrame f in GuessGameFrame class because GuessGameFrame is already a JFrame :

And update your code:

f = new JFrame("Guessing game"); to this.setTitle("Guessing game");

f.add(p); to this.getContentPane().add(p);