Custom component not visible initially, but then becomes visible

Question

I've come across an issue when messing around with shapes. I created a simple program with a slider with which you manipulate the size of an arc. The problem is that when I run it, the arc isn't painted to the screen. However, when I change the value of the slider, everything starts working perfectly. Any thoughts on what this might be caused by? Here's the code:

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeListener;
import javax.swing.event.ChangeEvent;
import java.awt.*;
import java.awt.geom.*;
@SuppressWarnings("serial")
public class GraphicsTest2 extends JFrame implements ChangeListener { // START OF GraphicsTest2
    private JPanel sliderPanel, thePanel;
    private JSlider slider;
    private DrawStuff draw;
    public static void main(String[] args) { // START OF main
        new GraphicsTest2();
    } // END OF main
    public GraphicsTest2() { // START OF CONSTRUCTOR
        super("Graphics test 2");
        this.setSize(500, 500);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        thePanel = new JPanel();
        thePanel.setLayout(new BorderLayout(10, 10));
        slider = new JSlider(JSlider.HORIZONTAL, 1, 360, 120);
        slider.addChangeListener(this);
        sliderPanel = new JPanel();
        sliderPanel.add(slider, BorderLayout.CENTER);
        draw = new DrawStuff();
        thePanel.add(sliderPanel, BorderLayout.SOUTH);
        thePanel.add(draw, BorderLayout.CENTER);
        this.add(thePanel, BorderLayout.CENTER);
        this.pack();
        this.validate();
        this.setVisible(true);
    } // END OF CONSTRUCTOR
    public void stateChanged(ChangeEvent e) { // START OF stateChanged
        if(e.getSource() == slider) {
            int size = slider.getValue();
            draw.arc = new Arc2D.Double(draw.getWidth() / 2 - 50, draw.getHeight() / 2 - 50, 100, 100, 0, size, Arc2D.PIE);
            this.repaint();
        }
    } // END OF stateChanged
    private class DrawStuff extends JComponent { // START OF DrawStuff
        Shape arc;
        public void paintComponent(Graphics g) { // START OF paintComponent
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g2.setColor(Color.GREEN);
            g2.fill(arc);
        } // END OF paintComponent
        public DrawStuff() {
            this.setPreferredSize(new Dimension(100, 140));
            arc = new Arc2D.Double(this.getWidth() / 2 - 50, this.getHeight() / 2 - 50, 100, 100, 0, 120, Arc2D.PIE);
        }
    } // END OF DrawStuff
} // END OF GraphicsTest2

Answer 1

When you create your arc in the constructor of DrawStuff here:

arc = new Arc2D.Double(this.getWidth() / 2 - 50, this.getHeight() / 2 - 50, 100, 100, 0, 120, Arc2D.PIE);

this.getWidth() and this.getHeight() will give a result of 0 because the components are not sized yet. A simple fix would be to use the fixed size like this:

arc = new Arc2D.Double(210 / 2 - 50, 140 / 2 - 50, 100, 100, 0, 120, Arc2D.PIE);