JFRAME, JPANEL. Making button and dropdown menu visible and on the right location

Question

Im trying to create a simple welcome screen where the user can choose with how many cards he wants to play a memory game. On the top of the screen I want a text ( I created a JLabel for this). Below that I want a dropdown menu and to the right of this dropdown a button. The code I have so far doenst display anything when I run it (besides a empty JFrame). What am I doing wrong?

The code:

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Main {

        public static void main(String[] args) {

            JFrame frame = new JFrame("Memory game");
            frame.setVisible(true);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(500, 500);
            frame.setLocation(430, 100);
            frame.setLayout(null);

            JPanel panel = new JPanel();

            frame.add(panel);

            JLabel lbl = new JLabel("How many cards u want to play with?");
            lbl.setVisible(true);
            lbl.setLocation(150,150);
            panel.add(lbl);

            String[] choices = { "8","12", "16","20","24","28","32"};

            final JComboBox<String> cb = new JComboBox<String>(choices);

            cb.setVisible(true);
            cb.setLocation(200,150);
            panel.add(cb);

            JButton btn = new JButton("Start game");
            btn.setLocation(175,200);
            panel.add(btn);

        }

}

Answer 1

You would need to set the size of your panel. One way to do it:

    JPanel panel = new JPanel();
    panel.setSize(frame.getSize());
    frame.add(panel);

But using

frame.setLayout(null);

Will give you a lot of headache if you dont know what you are doing (if you had a layout, you wouldnt have had this problem). You should always use a layout. Have a look at the official Visual Guide to Layout Managers . Though there are more you can download from the web.

Also another advice: If you are just starting to learn how to build Desktop Applications, maybe you should skip swing and get to JavaFX directly. This will save you even more headache.