Looped drawString not appearing in JFrame

Question

I am trying to create a JFrame that displays a string in every even-numbered font size from 4 to 24. To do this I am trying to do a for loop that creates a drawString that uses a Font that increases in +2 font size everytime. Trying to get the next drawString placed just underneath the previous by getting the getHeight() of the previous and adding it to the varaible y. However the JFrame is empty when the program is run. Where have I gone wrong?

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

public class JFontSizeDemo extends JFrame {
    int x = 10;
    int y = 40;
    int heightOfFont;
    public void paint(Graphics g) {
        super.paint(g);
        for(int size = 4; size <= 24; size += 2) {
            g.setFont(new Font("Arial", Font.BOLD, size));
            g.drawString("Name", x, y);
            heightOfFont = g.getFontMetrics().getHeight();
            y += heightOfFont;
        }
    }
    public static void main(String[] args) {
            JFontSizeDemo frame = new JFontSizeDemo();
            frame.setSize(300, 300);
            frame.setVisible(true);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

Answer 1

Don't paint directly on JFrame, which is a top level container. Use JComponent or JPanel. Override paintComponent() for painting rather than paint().

Take a look at Performing Custom Painting tutorial for more details and examples.

Here is an slightly modified example of your code:

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

public class FontSizeDemo {
    private static void createAndShowUI() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                int y = 0;
                for(int size = 4; size <= 24; size += 2) {
                    g.setFont(new Font("Arial", Font.BOLD, size));
                    g.drawString("Name", 0, y);
                    int heightOfFont = g.getFontMetrics().getHeight();
                    y += heightOfFont;
                }
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(300, 300); 
            }
        };

        frame.add(panel);
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        frame.pack();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowUI();
            }
        });
    }
}

Other than the introduction of JPanel for painting, there is a quick tiny fix of y coordinate, to ensure text remains in the same place after repaint. There is also SwingUtilities.invokeLater. Also, usually there is no need to extend JFrame at all.