How do I restart Snake game (Java)? [closed]

I’m a beginner so I used Bro Code’s (a YouTuber) version of snake game. It’s almost identical with minor adjustments, but I’ve been trying to figure out how to restart the game when I die. I’ve tried making a restart button and tried to make it restart with a keystroke but I’ve got no experience coding so I couldn’t figure it out. Here’s the source code:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.Random;

import javax.swing.JPanel;
import javax.swing.Timer;

public class GamePanel<Restart> extends JPanel implements ActionListener {
    static final int SCREEN_WIDTH = 1300;
    static final int SCREEN_HEIGHT = 750;
    static final int UNIT_SIZE = 25;
    static final int GAME_UNITS = (SCREEN_WIDTH * SCREEN_HEIGHT) / (UNIT_SIZE * UNIT_SIZE);
    static final int DELAY = 85;
    final int x[] = new int[GAME_UNITS];
    final int y[] = new int[GAME_UNITS];
    int bodyParts = 5;
    int applesEaten;
    int appleX;
    int appleY;
    char direction = 'R';
    boolean running = false;
    Timer timer;
    Random random;

    GamePanel() {
        random = new Random();
        this.setPreferredSize(new Dimension(SCREEN_WIDTH, SCREEN_HEIGHT));
        this.setBackground(Color.black);
        this.setFocusable(true);
        this.addKeyListener(new MyKeyAdapter());
        startGame();
    }

    public void startGame() {
        newApple();
        running = true;
        timer = new Timer(DELAY, this);
        timer.start();
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        draw(g);
    }

    public void draw(Graphics g) {
        if (running) {
            /*
             * for(int i=0;i<SCREEN_HEIGHT/UNIT_SIZE;i++) { g.drawLine(i*UNIT_SIZE, 0,
             * i*UNIT_SIZE, SCREEN_HEIGHT); g.drawLine(0, i*UNIT_SIZE, SCREEN_WIDTH,
             * i*UNIT_SIZE); }
             */
            g.setColor(Color.red);
            g.fillOval(appleX, appleY, UNIT_SIZE, UNIT_SIZE);
            for (int i = 0; i < bodyParts; i++) {
                if (i == 0) {
                    g.setColor(Color.green);
                    g.fillRect(x[i], y[i], UNIT_SIZE, UNIT_SIZE);
                }
                else {
                    g.setColor(new Color(45, 180, 0));
                    // g.setColor(new
                    // Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)));
                    g.fillRect(x[i], y[i], UNIT_SIZE, UNIT_SIZE);
                }
            }
            g.setColor(Color.red);
            g.setFont(new Font("Ink Free", Font.BOLD, 40));
            FontMetrics metrics = getFontMetrics(g.getFont());
            g.drawString("Score: " + applesEaten,
                    (SCREEN_WIDTH - metrics.stringWidth("Score: " + applesEaten)) / 2,
                    g.getFont().getSize());
        }
        else {
            gameOver(g);
        }
    }

    public void newApple() {
        appleX = random.nextInt((int) (SCREEN_WIDTH / UNIT_SIZE)) * UNIT_SIZE;
        appleY = random.nextInt((int) (SCREEN_HEIGHT / UNIT_SIZE)) * UNIT_SIZE;
    }

    public void move() {
        for (int i = bodyParts; i > 0; i--) {
            x[i] = x[i - 1];
            y[i] = y[i - 1];
        }
        switch (direction) {
            case 'U':
                y[0] = y[0] - UNIT_SIZE;
                break;
            case 'D':
                y[0] = y[0] + UNIT_SIZE;
                break;
            case 'L':
                x[0] = x[0] - UNIT_SIZE;
                break;
            case 'R':
                x[0] = x[0] + UNIT_SIZE;
                break;
        }
    }

    public void checkApple() {
        if ((x[0] == appleX) && (y[0] == appleY)) {
            bodyParts++;
            applesEaten++;
            newApple();
        }
    }

    public void checkCollisions() {
        // checks if head collides with body
        for (int i = bodyParts; i > 0; i--) {
            if ((x[0] == x[i]) && (y[0] == y[i])) {
                running = false;
            }
        }
        // check if head touches left border
        if (x[0] < 0) {
            running = false;
        }
        // check if head touches right border
        if (x[0] > SCREEN_WIDTH) {
            running = false;
        }
        // check if head touches top border
        if (y[0] < 0) {
            running = false;
        }
        // check if head touches bottom border
        if (y[0] > SCREEN_HEIGHT) {
            running = false;
        }
        if (!running) {
            timer.stop();
        }
    }

    public void gameOver(Graphics g) {
        // Score
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free", Font.BOLD, 40));
        FontMetrics metrics1 = getFontMetrics(g.getFont());
        g.drawString("Score: " + applesEaten,
                (SCREEN_WIDTH - metrics1.stringWidth("Score: " + applesEaten)) / 2,
                g.getFont().getSize());
        // Game Over text
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free", Font.BOLD, 75));
        FontMetrics metrics2 = getFontMetrics(g.getFont());
        g.drawString("Game Over", (SCREEN_WIDTH - metrics2.stringWidth("Game Over")) / 2,
                SCREEN_HEIGHT / 2);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (running) {
            move();
            checkApple();
            checkCollisions();
        }
        repaint();
    }

    public class MyKeyAdapter extends KeyAdapter {
        @Override
        public void keyPressed(KeyEvent e) {
            switch (e.getKeyCode()) {
                case KeyEvent.VK_A:
                    if (direction != 'R') {
                        direction = 'L';
                    }
                    break;
                case KeyEvent.VK_D:
                    if (direction != 'L') {
                        direction = 'R';
                    }
                    break;
                case KeyEvent.VK_W:
                    if (direction != 'D') {
                        direction = 'U';
                    }
                    break;
                case KeyEvent.VK_S:
                    if (direction != 'U') {
                        direction = 'D';
                    }
            }
        }
    }
}

Answer

This is the solution, Pressing Enter will close the previous window and open a new game window. Let me know if you don’t understand something so I can explain it to you!

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.Random;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public final class GamePanel<Restart> extends JPanel implements ActionListener {
    
    JFrame frame = new JFrame();
    JPanel panel = new JPanel();
  
    static final int SCREEN_WIDTH = 1300;
    static final int SCREEN_HEIGHT = 750;
    static final int UNIT_SIZE = 25;
    static final int GAME_UNITS = (SCREEN_WIDTH * SCREEN_HEIGHT) / (UNIT_SIZE * UNIT_SIZE);
    static final int DELAY = 85;
    final int x[] = new int[GAME_UNITS];
    final int y[] = new int[GAME_UNITS];
    int bodyParts = 5;
    int applesEaten;
    int appleX;
    int appleY;
    char direction = 'R';
    boolean running = false;
    Timer timer;
    Random random;

    public void createGUI() {
        panel.add(new GamePanel());
        frame.add(panel);
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    }

    GamePanel() {
        random = new Random();
        setPreferredSize(new Dimension(SCREEN_WIDTH, SCREEN_HEIGHT));
        setBackground(Color.black);
        setFocusable(true);
        addKeyListener(new MyKeyAdapter());
        startGame();
    }

    public void startGame() {
        newApple();
        running = true;
        timer = new Timer(DELAY, this);
        timer.start();
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        draw(g);
    }

    public void draw(Graphics g) {
        if (running) {
            /*
             * for(int i=0;i<SCREEN_HEIGHT/UNIT_SIZE;i++) { g.drawLine(i*UNIT_SIZE, 0,
             * i*UNIT_SIZE, SCREEN_HEIGHT); g.drawLine(0, i*UNIT_SIZE, SCREEN_WIDTH,
             * i*UNIT_SIZE); }
             */
            g.setColor(Color.red);
            g.fillOval(appleX, appleY, UNIT_SIZE, UNIT_SIZE);
            for (int i = 0; i < bodyParts; i++) {
                if (i == 0) {
                    g.setColor(Color.green);
                    g.fillRect(x[i], y[i], UNIT_SIZE, UNIT_SIZE);
                } else {
                    g.setColor(new Color(45, 180, 0));
                    // g.setColor(new
                    // Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)));
                    g.fillRect(x[i], y[i], UNIT_SIZE, UNIT_SIZE);
                }
            }
            g.setColor(Color.red);
            g.setFont(new Font("Ink Free", Font.BOLD, 40));
            FontMetrics metrics = getFontMetrics(g.getFont());
            g.drawString("Score: " + applesEaten,
                    (SCREEN_WIDTH - metrics.stringWidth("Score: " + applesEaten)) / 2,
                    g.getFont().getSize());
        } else {
            gameOver(g);
        }
    }

    public void newApple() {
        appleX = random.nextInt((int) (SCREEN_WIDTH / UNIT_SIZE)) * UNIT_SIZE;
        appleY = random.nextInt((int) (SCREEN_HEIGHT / UNIT_SIZE)) * UNIT_SIZE;
    }

    public void move() {
        for (int i = bodyParts; i > 0; i--) {
            x[i] = x[i - 1];
            y[i] = y[i - 1];
        }
        switch (direction) {
            case 'U':
                y[0] = y[0] - UNIT_SIZE;
                break;
            case 'D':
                y[0] = y[0] + UNIT_SIZE;
                break;
            case 'L':
                x[0] = x[0] - UNIT_SIZE;
                break;
            case 'R':
                x[0] = x[0] + UNIT_SIZE;
                break;
        }
    }

    public void checkApple() {
        if ((x[0] == appleX) && (y[0] == appleY)) {
            bodyParts++;
            applesEaten++;
            newApple();
        }
    }

    public void checkCollisions() {
        // checks if head collides with body
        for (int i = bodyParts; i > 0; i--) {
            if ((x[0] == x[i]) && (y[0] == y[i])) {
                running = false;
            }
        }
        // check if head touches left border
        if (x[0] < 0) {
            running = false;
        }
        // check if head touches right border
        if (x[0] > SCREEN_WIDTH) {
            running = false;
        }
        // check if head touches top border
        if (y[0] < 0) {
            running = false;
        }
        // check if head touches bottom border
        if (y[0] > SCREEN_HEIGHT) {
            running = false;
        }
        if (!running) {
            timer.stop();
        }
    }

    public void gameOver(Graphics g) {
        // Score
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free", Font.BOLD, 40));
        FontMetrics metrics1 = getFontMetrics(g.getFont());
        g.drawString("Score: " + applesEaten,
                (SCREEN_WIDTH - metrics1.stringWidth("Score: " + applesEaten)) / 2,
                g.getFont().getSize());
        // Game Over text
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free", Font.BOLD, 75));
        FontMetrics metrics2 = getFontMetrics(g.getFont());
        g.drawString("Game Over", (SCREEN_WIDTH - metrics2.stringWidth("Game Over")) / 2,
                SCREEN_HEIGHT / 2);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (running) {
            move();
            checkApple();
            checkCollisions();
        }
        repaint();
    }
    
    public void closeRunningWindow(KeyEvent e) {
        JComponent comp = (JComponent) e.getSource();
        Window win = SwingUtilities.getWindowAncestor(comp);
        win.dispose();
    }
    
    public void startAgain() {
        EventQueue.invokeLater(() -> {
            GamePanel game = new GamePanel();
            game.createGUI();
        });
    }

    public class MyKeyAdapter extends KeyAdapter {

        @Override
        public void keyPressed(KeyEvent e) {
            switch (e.getKeyCode()) {
                case KeyEvent.VK_A:
                    if (direction != 'R') {
                        direction = 'L';
                    }
                    break;
                case KeyEvent.VK_D:
                    if (direction != 'L') {
                        direction = 'R';
                    }
                    break;
                case KeyEvent.VK_W:
                    if (direction != 'D') {
                        direction = 'U';
                    }
                    break;
                case KeyEvent.VK_S:
                    if (direction != 'U') {
                        direction = 'D';
                    }
                    break;
                case KeyEvent.VK_ENTER:
                    closeRunningWindow(e);
                    startAgain();
                    break;
            }
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            GamePanel game = new GamePanel();
            game.createGUI();
        });
    }
}