JTextField not appearing in grid layout

Question

I'm using a grid layout for one of my programs and when i try to add JTextFields to the grid It doesn't show at all. If i try adding JButtons instead of JTextFields in the same method it works perfectly.

    package suDUKO;

import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Toolkit;

import javax.swing.JTextField;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
public class Gui_Class {
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    Dimension blocksize;
    private final  int screenW=(int) (screenSize.getWidth()/2);
    private final  int screenH=(int) (screenSize.getHeight()/2);
    JFrame frame;
    JPanel panel;

        public Gui_Class() {
            frame=new JFrame("Suduko");
            frame.setBounds((int) screenW-500,screenH-500,500,500);
            frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            frame.setVisible(true);
            panel=new JPanel();
            frame.add(panel);
            panel.setVisible(true);

            panel.setLayout(new GridLayout(9, 9));
            JTextField [][] table = new JTextField[9][9];
            for(int m = 0; m < 9; m++) {
                   for(int n = 0; n < 9; n++) {
                      table[m][n]=new JTextField(m+" "+n);
                      table[m][n].setVisible(true);
                      panel.add(table[m][n]);

                   }
                }
    }
}

Answer 1

There are a number of problems with this code. The main ones that you asked about, can be fixed by adding all the components, then calling pack() before finally calling setVisible(true);.

If the code as seen above does those things, the GUI won't be 500 x 500 in size, and will not be centered. Each has it's own best approach.

Firstly, it seems you want the content pane to be square (500 x 500), and that won't happen if the frame is 500 x 500, because it has a title bar and possibly borders to render. Then centering a GUI on screen is as simple as frame.setLocationRelativeTo(null).

You've already marked this correct, but was just preparing an example of what is written above, so here it is!

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

public class Gui_Class {

    JFrame frame;
    JPanel panel;

    public Gui_Class() {
        frame = new JFrame("Suduko");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        panel = new JPanel(new GridLayout(9, 9));
        frame.add(panel);
        //panel.setVisible(true); //unnecessary 

        JTextField[][] table = new JTextField[9][9];
        for (int m = 0; m < 9; m++) {
            for (int n = 0; n < 9; n++) {
                table[m][n] = new SquareTextField(m + " " + n);
                panel.add(table[m][n]);
            }
        }

        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        Runnable r = () -> {
            new Gui_Class();
        };
        SwingUtilities.invokeLater(r);
    }
}

class SquareTextField extends JTextField {

    int size = 30;

    SquareTextField(String s) {
        super(s);
        setFont(getFont().deriveFont((float)size));
        int sz = size/6;
        setMargin(new Insets(sz, sz, sz, sz));
    }

    @Override
    public Dimension getPreferredSize() {
        Dimension d = super.getPreferredSize();
        int w = d.width;
        int h = d.height;
        int max = w>h ? w : h;

        return new Dimension(max, max);
    }
}