为什么 repaint() 不在 swing 计时器中调用paintcomponent？

Question

When I use repaint() in the swing timer method startTimer, it just simply doesnt call paintcomponent(). Everything works inside of the timer method except repaint(). Im pretty new at java so if anyone could help me with this problem or point out any other errors I would greatly appreciate it. thank you

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Scanner;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class Board extends JPanel {
    Timer timer;
    int count;
    int clockNumber;
    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.fillRect(30, 30, 640, 640);//makes a black square
        for(int i=30;i<=510; i+=160)//adds white columns
        {
            for(int j=30; j<=510; j+=160)
            {
                g.clearRect(i,  j,  80,  80);
            }
        }
        for(int i=110; i<=590; i+=160)//adds black columns
        {
            for(int j=110; j<=590; j+=160)
            {
                g.clearRect(i, j, 80, 80);
            }
        }
        g.setFont(new Font("Monospace", Font.BOLD, 30));
        g.setColor(Color.WHITE);
        g.drawString("a", 85, 660);
        g.drawString("c", 245, 660);
        g.drawString("e", 405, 660);
        g.drawString("g", 565, 660);
        g.drawString("7", 35, 140);
        g.drawString("5", 35, 300);
        g.drawString("3", 35, 460);
        g.drawString("1", 35, 620);
        
        g.setColor(Color.BLACK);
        g.drawString("b", 165, 660);
        g.drawString("d", 325, 660);
        g.drawString("f", 485, 660);
        g.drawString("h", 645, 660);
        g.drawString("8", 35, 60);
        g.drawString("6", 35, 220);
        g.drawString("4", 35, 380);
        g.drawString("2", 35, 540);
        System.out.println(clockNumber);
        g.drawString(String.valueOf(clockNumber), 300, 300);
    }
    public void showX(Graphics g)
    {
        g.setFont(new Font("wrongFont", Font.BOLD, 200)); 
        g.setColor(Color.RED);
        g.drawString("X", 35, 540);
    }
    public void boardImage()
    {
        JFrame frame=new JFrame();
        frame.setSize(600, 600);
        frame.getContentPane().add(new Board());
        frame.setLocationRelativeTo(null);
        frame.setBackground(Color.LIGHT_GRAY);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        CoordinateGame game=new CoordinateGame();
        frame.addMouseListener(new MouseAdapter() 
        {
            public void mouseClicked(MouseEvent e) 
            {
                int x=e.getX();
                int y=e.getY();
                    
            }
        }); 
    }
    public int clockNumber()
    {
        return clockNumber;
    }
    public void startTimer(int seconds)
    {
        ActionListener action=new ActionListener()
        {
            public void actionPerformed(ActionEvent e) 
            {
                clockNumber=count;
                if(count==0)
                {
                    timer.stop();
                }
                else
                {
                    System.out.println(count);
                    clockNumber--;
                    count--;
                    repaint();
                }
            }
            
        };
        timer=new Timer(1000, action);
        timer.setInitialDelay(0);
        timer.start();
        count=seconds;
    }   
}

Answer 1

Since you didn't provide a runnable example I should suppose that you're doing something like

Board board=new Board();
board.boardImage();
board.startTimer();

The problem is in boardImage() that creates a new instance of Board and adds that instance to the JFrame, not the original board , on which you start the timer.

So replace

frame.getContentPane().add(new Board());

with

frame.getContentPane().add(this);

Consider also removing the explicit setSize on the frame and add override getPreferredSize on your custom component, then use frame.pack() to automatically adjust the frame size to the board.