Graphics2D on JPanel and adding JPanel to JFrame

Question

I am trying to draw on a JPanel and add it to a JFrame in my createAndShowGui method. I have tried a few different things: creating the JPanel in the createAndShowGui method, adding the drawing to the JFrame, etc... The one thing that is common, I don't see any of my graphics!

Note: I am able to get the graphics to display in a JTabbedPane but not on a JPanel, which is what I actually want them to show up on to make the code more object oriented.

Edit: Here is the working concept self contained example:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class DrawPanelMain extends JPanel {

    /*
    * Variables used to set the value of preferred height and width
    */
    public static final double version = 0.0;
    JPanel switchPanel = new JPanel();
    JPanel testPanel = new JPanel();
    JPanel btnPanel = new JPanel();
    DrawEllipses drawEllipses = new DrawEllipses(POINT_LIST);

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                initializePointList();
                createAndShowGui();
            }
        });
    }

    public static java.util.List<Point> POINT_LIST = new ArrayList<>();

    /*
    * This loop will initialize POINT_LIST with the set of points for drawing the ellipses.
    * The for each loop initializes points for the top row and the second for loop draws the
    * right triangle.
    */
    public static void initializePointList() {

        int ellipsePointsYCoordinate[] = {140, 200, 260, 320, 380, 440, 500, 560, 620};
        int ellipsePointsXCoordinate[] = {140, 200, 260, 320, 380, 440, 500, 560, 620, 680};
        int xx = 80;

        for (int aXt : ellipsePointsXCoordinate) {
            POINT_LIST.add(new Point(aXt, xx));
        }

        for (int i = 0; i < ellipsePointsYCoordinate.length; i++) {
            for (int j = i; j < ellipsePointsYCoordinate.length; j++) {
                POINT_LIST.add(new Point(ellipsePointsXCoordinate[i], ellipsePointsYCoordinate[j]));
            }
        }
    }

    public DrawPanelMain() {

        testPanel.setBackground(Color.RED);
        switchPanel.add(drawEllipses);

        setLayout(new BorderLayout());
        add(switchPanel, BorderLayout.CENTER);
        add(testPanel, BorderLayout.EAST);
        add(btnPanel, BorderLayout.SOUTH);
        getPreferredSize();

        btnPanel.add(new JButton(new AddSwitchAction("Add Switch Panel")));
    }

    public static void createAndShowGui() {

        JFrame frame = new JFrame("RF Connection Panel " + version);

        frame.setLayout(new BorderLayout());
        frame.add(new DrawPanelMain());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationByPlatform(false);
        //frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setVisible(true);
    }

    /*
    * AddSwitchAction will add a new pane to the tabbedPane when the add switch button is clicked
    */
    private class AddSwitchAction extends AbstractAction {
        public AddSwitchAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            int index = 0;
            DrawEllipses tabComponent = new DrawEllipses(POINT_LIST);
            switchPanel.add(tabComponent, index++);

        }
    }

}

@SuppressWarnings("serial")
class DrawEllipses extends JPanel {
    private final int PREF_W = 750; //Window width
    private final int PREF_H = 750; //Window height
    private static final int OVAL_WIDTH = 30;
    private static final Color INACTIVE_COLOR = Color.RED;
    private static final Color ACTIVE_COLOR = Color.green;
    private java.util.List<Point> points;
    private java.util.List<Ellipse2D> ellipses = new ArrayList<>();
    private Map<Ellipse2D, Color> ellipseColorMap = new HashMap<>();

    /*
     * This method is used to populate "ellipses" with the initialized ellipse2D dimensions
     */
    public DrawEllipses(java.util.List<Point> points) {
        this.points = points;
        for (Point p : points) {
            int x = p.x - OVAL_WIDTH / 2;
            int y = p.y - OVAL_WIDTH / 2;
            int w = OVAL_WIDTH;
            int h = OVAL_WIDTH;
            Ellipse2D ellipse = new Ellipse2D.Double(x, y, w, h);
            ellipses.add(ellipse);
            ellipseColorMap.put(ellipse, INACTIVE_COLOR);
        }

        MyMouseAdapter mListener = new MyMouseAdapter();
        addMouseListener(mListener);
        addMouseMotionListener(mListener);
    }

    /*
     * paintComponent is used to paint the ellipses
     */
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        for (Ellipse2D ellipse : ellipses) {
            g2.setColor(ellipseColorMap.get(ellipse));
            g2.fill(ellipse);
            g2.setColor(Color.BLACK);
            g2.setStroke(new BasicStroke(2));
            g2.draw(ellipse);
        }

        /*
         * Set the font characteristics, color, and draw the row labels.
         */
        g.setFont(new Font("TimesRoman", Font.BOLD, 18));
        g.setColor(Color.BLACK);

        //Along the top row
        g.drawString("External Port", 10, 50);
        g.drawString("1", 135, 50);
        g.drawString("2", 195, 50);
        g.drawString("3", 255, 50);
        g.drawString("4", 315, 50);
        g.drawString("5", 375, 50);
        g.drawString("6", 435, 50);
        g.drawString("7", 495, 50);
        g.drawString("8", 555, 50);
        g.drawString("9", 615, 50);
        g.drawString("10", 672, 50);

        //Along the Y-axis
        g.drawString("Radio 2", 40, 145);
        g.drawString("3", 90, 205);
        g.drawString("4", 90, 265);
        g.drawString("5", 90, 325);
        g.drawString("6", 90, 385);
        g.drawString("7", 90, 445);
        g.drawString("8", 90, 505);
        g.drawString("9", 90, 565);
        g.drawString("10", 90, 625);

        //Along the X-Axis
        g.drawString("1", 135, 670);
        g.drawString("2", 195, 670);
        g.drawString("3", 255, 670);
        g.drawString("4", 315, 670);
        g.drawString("5", 375, 670);
        g.drawString("6", 435, 670);
        g.drawString("7", 495, 670);
        g.drawString("8", 555, 670);
        g.drawString("9", 615, 670);

        //Draws a 3DRect around the top row of ellipse2D objects
        g2.setColor(Color.lightGray);
        g2.draw3DRect(120, 60, 580, 40, true);
        g2.draw3DRect(121, 61, 578, 38, true);
        g2.draw3DRect(122, 62, 576, 36, true);

    }

    /*
     * MouseAdapter is extended for mousePressed Event that detects if the x, y coordinates
     * of a drawn ellipse are clicked.  If the color is INACTIVE it is changed to ACTIVE and
     * vice versa.
     */
    private class MyMouseAdapter extends MouseAdapter {
        @Override
        /*
         * When mousePressed event occurs, the color is toggled between ACTIVE and INACTIVE
         */
        public void mousePressed(MouseEvent e) {
            Color c;
            for (Ellipse2D ellipse : ellipses) {
                if (ellipse.contains(e.getPoint())) {
                    c = (ellipseColorMap.get(ellipse) == INACTIVE_COLOR) ? ACTIVE_COLOR : INACTIVE_COLOR;
                    ellipseColorMap.put(ellipse, c);
                }
            }
            repaint();
        }
    }

    /*
* This method will set the dimensions of the JFrame equal to the preferred H x W
*/
    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }
}

Answer 1

switchPanel.add(title, tabComponent);

By default a JPanel uses a FlowLayout which respects the preferred size of the component. The preferred size of your component is (0, 0) so there is nothing to paint. Also, you are using the "title" string which is incorrect (and obsolete as has already been mentioned). That string represents a constraint for the layout manager. You can't just make up a String value. In any case FlowLayout does not accept any contraints so you should just be using:

switchPanel.add(tabComponent);

I am trying to draw on a JPanel

When doing custom painting you need to override the getPreferredSize() of the panel so the layout manager can use the information. If you don't override this method then the size is (0, 0) so there is nothing to paint.

Edit:

First some general comments:

1. Don't hardcode sizes of the panel. Your hardcoded size of (1200 x 750) is too large for my monitor. If you want full screen then use frame.setExtendedState(JFrame.MAXIMIZED_BOTH);

2. Post code that you are actually testing. As has already been mentioned your posted code doesn't even add the "switchPanel" to the frame.

3. You haven't updated the code to show how you override the getPreferredSize() method.

Finally, I see in your code that you add the panel dynamically to the visible GUI. In this case the general code should be:

panel.add(....);
panel.revalidate(); // to invoke the layout manager otherwise size is still (0, 0)
panel.repaint();

Answer 2

You are adding DrawEllipses instances to switchPanel using an obsolete method add(String,Component); you should use something like add(component, index). Also, You don't add switchPanel to anything (commented out in DrawPanelMain ctor).