Adding a JPanel to another JPanel having TableLayout

Question

I am trying to develop a map editor in Java using TableLayout. My map window receives as a constructor a Map object. From that map object i am able to retrieve the Grid and every item in the grid along with other getters and setters. The problem is that even though the Mapping extends JComponent, when I place it in a panel it is not painted. I have overridden the paint method to satisfy my needs. Here is the code, maybe you could help me.

public class MapTest extends JFrame implements ActionListener {

    private JPanel mainPanel;
    private JPanel mapPanel;
    private JPanel minimapPanel;
    private JPanel relationPanel;
    private TableLayout tableLayout;
    private JPanel tile;

    MapTest(Map map) {
        mainPanel = (JPanel) getContentPane();
        mapPanel = new JPanel();
        populateMapPanel(map);
        mainPanel.add(mapPanel);
        this.setPreferredSize(new Dimension(800, 600));
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    private double[][] generateTableLayoutSize(int x, int y, int size) {
        double panelSize[][] = new double[x][y];
        for (int i = 0; i < x; i++) {
            for (int j = 0; j < y; j++) {
                panelSize[i][j] = size;
            }
        }
        return panelSize;
    }

    private void populateMapPanel(Map map) {
        double[][] layoutSize = generateTableLayoutSize(map.getMapGrid().getRows(), map.getMapGrid().getColumns(), 50);
        tableLayout = new TableLayout(layoutSize);

        for(int i = 0; i < map.getMapGrid().getRows(); i++)
        {
            for(int j = 0; j < map.getMapGrid().getColumns(); j++)
            {
                tile = new JPanel();
                tile.setName(String.valueOf(((Mapping)map.getMapGrid().getItem(i, j)).getCharacter()));
                tile.add(map.getMapItem(i, j));
                String constraint = i + "," + j;
                mapPanel.add(tile, constraint);
            }
        }
        mapPanel.validate();
        mapPanel.repaint();
    }

    public void actionPerformed(ActionEvent e) {
        throw new UnsupportedOperationException("Not supported yet.");
    }
} 

My Mapping Class

public class Mapping extends JComponent implements Serializable{

    private BufferedImage image;
    private Character character;

    //default
    public Mapping() {
        super();
        this.image = null;
        this.character = '\u0000';
    }

    //Mapping from image and char
    public Mapping(BufferedImage image, char character) {
        super();
        this.image = image;
        this.character = character;
    }

    //Mapping from file and char
    public Mapping(File file, char character) {
        try {
            this.image = ImageIO.read(file);
            this.character = character;
        } catch (IOException ex) {
            System.out.println(ex);
        }
    }

    public char getCharacter() {
        return character;
    }

    public void setCharacter(char character) {
        this.character = character;
    }

    public BufferedImage getImage() {
        return image;
    }

    public void setImage(BufferedImage image) {
        this.image = image;
        repaint();
    }

    @Override
    /*Two mappings are consider the same if
    -they have the same image OR
    -they have the same character OR
    -both of the above*/
    public boolean equals(Object mapping) {
        if (this == mapping) {
            return true;
        }
        if (mapping instanceof Mapping) {
            return true;
        }
        //WARNING! equals might not work for images
        return (this.getImage()).equals(((Mapping) mapping).getImage())
                || (this.getCharacter()) == (((Mapping) mapping).getCharacter());
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        //g.drawImage(image, 0, 0, null);
        g.drawImage(image, 0, 0, this.getWidth(), this.getHeight(), null);
    }

//    @Override
//    public Dimension getPreferredSize() {
//        if (image == null) {
//            return new Dimension(10, 10); //instead of 100,100 set any prefered dimentions
//        } else {
//            return new Dimension(100, 100);//(image.getWidth(null), image.getHeight(null));
//        }
//    }
    private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException {
        character = (Character) in.readObject();
        image = ImageIO.read(ImageIO.createImageInputStream(in));
    }

    private void writeObject(java.io.ObjectOutputStream out) throws IOException {
        out.writeObject(character);
        ImageWriter writer = (ImageWriter) ImageIO.getImageWritersBySuffix("jpg").next();
        writer.setOutput(ImageIO.createImageOutputStream(out));
        ImageWriteParam param = writer.getDefaultWriteParam();
        param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        param.setCompressionQuality(0.85f);
        writer.write(null, new IIOImage(image, null, null), param);
    }
}

Answer 1

By default a JComponent has no preferred size. So when you add it to another panel there is nothing to paint.

Invoking the drawImage() method does not give a size to the component.

I don't know how TableLayout works, but I would try setting the preferred size of your component, then I'm guessing TableLayout will be able to work properly.

Or, maybe you should be using a GridLayout, which will automatically resize each grid based on the total space available.