Swing gui not displaying, but no errors?

Question

I am working on a java program that solves sudoku puzzles. So far all I have coded is a class that draws the board with swing, and another class that calls the gui class.

When I try and run the program nothing happens. No error messages are shown, but the gui doesn't show either. It immediately terminates.

Here is my code so far:

Gui class:

package sudoku;

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

public class Gui {

    Gui gui;
    JPanel board;
    JPanel subBoard[][];
    GridLayout layout;
    JLabel square[][];

    public void load() {

        gui = new Gui();
        gui.setUp();
        gui.buildBoard();

    }

    private void setUp() {

        layout = new GridLayout(3, 3);
        board = new JPanel(layout);
        subBoard = new JPanel[3][3];
        square = new JLabel[9][9];

    }

    private void buildBoard() {

        // set up board
        board.setSize(800, 600);
        board.setVisible(true);

        int mod = 0;
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {

                // add subBoards to board
                subBoard[i][j] = new JPanel();
                board.add(subBoard[i][j]);
                subBoard[i][j].setLayout(layout);
                subBoard[i][j].setVisible(true);

                // add textfields to each subBoard
                square[i + mod][j + mod] = new JLabel();
                subBoard[i][j].add(square[i + mod][j + mod]);
                square[i + mod][j + mod].setVisible(true);

            }
            mod += 3;

        }
    }

}

main class:

package sudoku;

public class SudokuSolver {

    public static void main(String[] args) {

        Gui gui = new Gui();
        gui.load();

    }

}

I tried running it in both eclipse and netbeans but got the same result both times. Why does this not work?

Answer 1

There is no displayable window such as a JFrame being used in the application.

EventQueue.invokeLater(new Runnable() {
   @Override
   public void run() {
      JFrame frame = new JFrame("New GUI");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      Gui gui = new Gui();
      gui.load();
      frame.add(gui.getBoard()); // add getBoard getter
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }
});

Remove the class member variable gui within Gui . This is shadowing variables in the outer class Gui so use the latter instead. Also override getPreferredSize to give the board a size when frame.pack() is invoked.

Answer 2

Make GUI extend JFrame firstly. Then in your main method call gui.setVisible(true); .

public class Gui extends JFrame { }

Then in main.

Gui gui = new Gui();
gui.load();
gui.setVisible(true);

Answer 3

You can not show directly Jpanel. for show gui you must use JFrame or any other Window class(JDialog, JWindow...) and after that set visible property true.

setVisible(true);

public class Gui extends JFrame {
       Gui(){
           ...
           setVisible(true);
           setSize(300,400);
        }
        ...
}