Question

I have this class which creates a grid:

 class GridPane extends JPanel{ 

    public GridPane(int row,int col){

      setLayout(new GridLayout(row,col));

      setBorder(BorderFactory.createEmptyBorder(1,1,1,1));

      for (int i =1; i<=(row*col); i++)
      {
         JPanel pan = new JPanel();
         pan.setBackground(Color.RED);
         pan.setPreferredSize(new Dimension(3,3));
         pan.setBorder(BorderFactory.createLineBorder(Color.BLACK));
         add(pan);
       } 
} 

And this which sets up the empty main frame with the group layout:

public MainFrame() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    GroupLayout gl_contentPane = new GroupLayout(contentPane);
    gl_contentPane.setHorizontalGroup(
        gl_contentPane.createParallelGroup(Alignment.LEADING)
            .addGap(0, 440, Short.MAX_VALUE)
    );
    gl_contentPane.setVerticalGroup(
        gl_contentPane.createParallelGroup(Alignment.LEADING)
            .addGap(0, 268, Short.MAX_VALUE)
    );
    contentPane.setLayout(gl_contentPane);
}

I am not very experienced with SWING and I have been trying to add a GridPane object to the Right of the Main Frame for some time. It keeps telling me something like :

java.lang.IllegalStateException: GridPane[,0,0,0×0,invalid,layout=java.awt.GridLayout,alignmentX=0.0,alignmentY=0.0,border=javax.swing.border.EmptyBorder@6ba7508a,flags=9,maximumSize=,minimumSize=,preferredSize=] is not attached to a vertical/horizontal group

Does anyone know what is going on? What should I do to accomplish what I need? Sorry for posting lots of code. Thanks for the help.

Answer 1

I would suggest that in this case you make use of BorderLayout.

contentPane = new JPanel();
contentPane.setLayout(new BorderLayout());

contentPane.add(pan, BorderLayout.LINE_END);

Here is the full code. I hope this is what you are looking for.

public class Main {

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setLayout(new BorderLayout());
        GridPane gp = new GridPane(5, 5);

        frame.add(gp, BorderLayout.EAST);

        frame.setVisible(true);
        frame.setSize(250, 250);
    }
}

class GridPane extends JPanel {

    public GridPane(int row, int col) {

        setLayout(new GridLayout(row, col));
        setPreferredSize(new Dimension(125, 125));
        setBorder(BorderFactory.createEmptyBorder(1, 1, 1, 1));

        for (int i = 1; i <= (row * col); i++) {
            JPanel pan = new JPanel();
            pan.setBackground(Color.RED);
            pan.setPreferredSize(new Dimension(3, 3));
            pan.setBorder(BorderFactory.createLineBorder(Color.BLACK));
            add(pan);
        }
    }
}

Useful links:

• A Visual Guide to Layout Managers
• How to Use BorderLayout
• How to Use GroupLayout