2D Game Programming Concepts

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

public class Game extends JPanel implements Runnable, KeyListener {
    private boolean running = true;
    private Player player;
    private Enemy enemy;
    private Thread gameThread;

    public Game() {
        player = new Player();
        enemy = new Enemy();
        this.addKeyListener(this);
        this.setFocusable(true);
        this.setFocusTraversalKeysEnabled(false);
        gameThread = new Thread(this);
        gameThread.start();
    }

    @Override
    public void run() {
        while (running) {
            update();
            repaint();
            try {
                Thread.sleep(16); // roughly 60 FPS
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private void update() {
        player.update();
        enemy.update();
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        player.render(g);
        enemy.render(g);
    }

    @Override
    public void keyPressed(KeyEvent e) {
        player.keyPressed(e);
    }

    @Override
    public void keyReleased(KeyEvent e) {
        player.keyReleased(e);
    }

    @Override
    public void keyTyped(KeyEvent e) {}

    public static void main(String[] args) {
        JFrame frame = new JFrame("2D Game");
        Game game = new Game();
        frame.add(game);
        frame.setSize(800, 600);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

class Player {
    private int x, y, velocityY;
    private boolean onGround = true, movingLeft = false, movingRight = false, jumping = false;
    private final int speed = 5, jumpStrength = 10, gravity = 1;

    public void update() {
        if (movingLeft) x -= speed;
        if (movingRight) x += speed;
        if (jumping && onGround) {
            velocityY = -jumpStrength;
            onGround = false;
        }
        y += velocityY;
        if (y >= 500) { // Assuming ground level is at y = 500
            y = 500;
            onGround = true;
            velocityY = 0;
        } else {
            velocityY += gravity;
        }
    }

    public void render(Graphics g) {
        g.fillRect(x, y, 50, 50); // Draw player as a rectangle
    }

    public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_LEFT) movingLeft = true;
        if (key == KeyEvent.VK_RIGHT) movingRight = true;
        if (key == KeyEvent.VK_SPACE) jumping = true;
    }

    public void keyReleased(KeyEvent e) {
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_LEFT) movingLeft = false;
        if (key == KeyEvent.VK_RIGHT) movingRight = false;
        if (key == KeyEvent.VK_SPACE) jumping = false;
    }
}

class Enemy {
    private int x, y;

    public void update() {
        // Enemy AI logic
    }

    public void render(Graphics g) {
        g.fillRect(x, y, 50, 50); // Draw enemy as a rectangle
    }
}