JLabel 未显示在我的 JButton 网格中

Question

Creating a game called reversi also known as Othello and I am trying to add the starting position of my Black and Whites counters (using JLabel , labelled 'W' and 'B' ) in the middle of the board diagonally opposite from each other but for some reason only 2 show up and the other 2 don't show, which I don't understand why.

How do I go about fixing it?

import java.io.*;
import java.util.*;
import java.lang.*;
import java.awt.*;
import javax.swing.*;

public class Reversi
{
    // instance variables - replace the example below with your own
    private JFrame frame;
    private JLabel userName1; 
    private JLabel userName2;
    private JTextField textUsername1;
    private JTextField textUsername2;
    private JButton startButton;
    private JButton [][] squares = new JButton[8][8];
    private JLabel whites = new JLabel("W");
    private JLabel blacks = new JLabel("B");
    
    /**
     * 
     */
    public Reversi()
    {
        // initialise instance variables
        gui();
        
    }

    /**
     * 
     */
    public void gui()
    {
        frame = new JFrame("Reversi Game");
        frame.setSize(800,800);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //frame.setLayout(new BoxLayout(frame, BoxLayout.X_AXIS));
        
        JPanel userInterface = new JPanel(new GridBagLayout());
        userInterface.setBackground(Color.LIGHT_GRAY);
        userInterface.setBorder(BorderFactory.createBevelBorder(0));
        //userInterface.setPreferredSize(new Dimension(350,700));
        GridBagConstraints c = new GridBagConstraints();
        //c.anchor = GridBagConstraints.NORTH;
        
        JPanel board = new JPanel();
        board.setBackground(Color.GRAY);
        board.setBorder(BorderFactory.createBevelBorder(1));
        board.setPreferredSize(new Dimension(750, 700));
        
        userName1 = new JLabel("Enter First player: ");
        userName2 = new JLabel("Enter Second player: ");
        textUsername1 = new JTextField(15);
        textUsername2 = new JTextField(15);
        startButton = new JButton("START");
        
        c.gridx = 0;
        c.gridy = 0; 
        userInterface.add(userName1, c);
        
        c.gridx = 1;
        userInterface.add(textUsername1, c);
        
        c.gridx = 0;
        c.gridy = 1;
        userInterface.add(userName2, c);
        
        c.gridx = 1;
        userInterface.add(textUsername2, c);
        
        c.gridx = 0;
        c.gridy = 2;
        c.gridwidth = 2;
        c.anchor = GridBagConstraints.SOUTH;
        userInterface.add(startButton, c);
        
        userInterface.setBorder(BorderFactory.createTitledBorder(
        BorderFactory.createEtchedBorder(), "Players/Scoreboard"));
        
        
        board.setLayout(new GridLayout(8,8));
        for(int i = 0; i< 8; i++){
            for (int j = 0; j < 8; j++)
             {
            squares[i][j] = new JButton();
            squares[i][j].setBackground(Color.GREEN);
            board.add(squares[i][j]);
            }
        }
        
        squares[4][3].add(blacks);
        squares[4][4].add(whites);
        squares[3][4].add(blacks);
        squares[3][3].add(whites);
        
        frame.add(board, BorderLayout.CENTER);
        JPanel wrapper = new JPanel();
        wrapper.add(userInterface);
        frame.add(wrapper, BorderLayout.LINE_END);
        
        makeMenuBar();
        frame.pack();
        frame.setVisible(true);
    }
    
    private void makeMenuBar()
    {
        //Finish coding later
        JMenuBar menubar = new JMenuBar();
        frame.setJMenuBar(menubar);
        
        JMenu fileMenu = new JMenu("File");
        menubar.add(fileMenu);
        
        JMenuItem saveFile = new JMenuItem("Save File");
        fileMenu.add(saveFile);
        
        JMenuItem quitGame = new JMenuItem("Quit");
        fileMenu.add(quitGame);
        quitGame.addActionListener(ev -> {quit(); });
        
    }
    
    
    private void quit()
    {
        System.exit(0);
    }
}

Answer 1

Each component (ie your JLabels ( whites and blacks )) can only be added to a container once, if you need to add more labels, even if they have the same String inside, you have to create a new object for those, otherwise these will be shown in the last container you've added them.

squares[4][3].add(blacks);
squares[4][4].add(whites);
squares[3][4].add(blacks); // Only this one is added
squares[3][3].add(whites); // Only this one is added

You'll need something like this, or have an array of JLabels and add them to all your squares , then just call yourJLabelArray[i][j].setText("W") (or "B" )

squares[4][3].add(new JLabel("B"));
squares[4][4].add(new JLabel("W"));
squares[3][4].add(new JLabel("B"));
squares[3][3].add(new JLabel("W"));