The game is not displayed, what should I do?

Question

Java

main.java:

package com.company;
        import javax.swing.*;

public class Main extends JFrame {
    public Main() {
        setTitle("Змейка");
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setSize(320,345);
        setLocation(400, 400);
        setVisible(true);
        add(new GameField());
    }
    public static void main(String[] args) {
        Main mw = new Main();
    }
}

GameField.java:

package com.company;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.Random;

public class GameField extends JPanel implements ActionListener {
    private final int size = 320;
    private final int dotSize = 16;
    private final int allDots = 400;
    private Image dot;
    private Image apple;
    private int appleX;
    private int appleY;
    private int[] x = new int[allDots];
    private int[] y = new int[allDots];
    private int dots;
    private Timer timer;
    private boolean left = false;
    private boolean right = true;
    private boolean up = false;
    private boolean down = false;
    private boolean inGame = true;

    public GameField() {
        setBackground(Color.black);
        loadImages();
        initGame();
        addKeyListener(new FieldKeyListener());
        setFocusable(true);
    }
    public void initGame() {
        dots = 3;
        for (int i = 0; i < dots; i++) {
            x[i] = 48 - i * dotSize;
            y[i] = 48;
        }
        timer = new Timer(250, this);
        timer.start();
        createApple();
    }
    public void createApple() {
        appleX = new Random().nextInt(20) * dotSize;
        appleY = new Random().nextInt(20) * dotSize;
    }

    public void loadImages() {
        ImageIcon iia = new ImageIcon("fruit.png");
        apple = iia.getImage();
        ImageIcon iid = new ImageIcon("dot.png");
        dot = iid.getImage();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (inGame) {
            g.drawImage(apple, appleX, appleY, this);
            for (int i = 0; i < dots; i++) {
                g.drawImage(dot, x[i], y[i], this);
            }
        } else {
            String str = "Game Over";
            Font font = new Font("Arial", 14, Font.BOLD);
            g.setColor(Color.red);
            g.setFont(font);
            g.drawString(str, 125, size / 2);
        }
    }

    public void move() {
        for (int i = dots; i > 0; i--) {
            x[i] = x[i-1];
            y[i] = y[i-1];
        }
        if (left) {
            x[0] -= dotSize;
        } else if (right) {
            x[0] += dotSize;
        } else if (up) {
            y[0] -= dotSize;
        } else if (down) {
            y[0] += dotSize;
        }
    }

    public void checkApple() {
        if (x[0] == appleX && y[0] == appleY) {
            dots++;
            createApple();
        }
    }

    public void checkCollisions() {
        for (int i = dots; i > 0; i--) {
            if (i > 4 && x[0] == x[i] && y[0] == y[i]) {
                inGame = false;
            }
        }
        if (x[0] > size) {
            inGame = false;
        } else if (x[0] < 0) {
            inGame = false;
        } else if (y[0] > size) {
            inGame = false;
        } else if (y[0] < 0) {
            inGame = false;
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (inGame) {
            checkApple();
            checkCollisions();
            move();
        }
        repaint();
    }
    class FieldKeyListener extends KeyAdapter {
        @Override
        public void keyPressed(KeyEvent e) {
            super.keyPressed(e);
            int key = e.getKeyCode();
            if (key == KeyEvent.VK_LEFT && !right) {
                left = true;
                up = false;
                down = false;
            } else if (key == KeyEvent.VK_RIGHT && !left) {
                right = true;
                up = false;
                down = false;
            } else if (key == KeyEvent.VK_UP && !down) {
                right = false;
                up = true;
                left = false;
            } else if (key == KeyEvent.VK_DOWN && !up) {
                right = false;
                left = false;
                down = true;
            }
        }
    }
}

Answer 1

Make setVisible(true)it the last line of the constructor.