GamePanel.java

package snakegame;

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

public class GamePanel extends JPanel implements ActionListener {

	static final int SCREEN_WIDTH = 600;
	static final int SCREEN_HEIGHT = 600;
	static final int UNIT_SIZE = 25;
	static final int GAME_UNITS = (SCREEN_WIDTH * SCREEN_HEIGHT) / UNIT_SIZE;
	static final int DELAY = 75;
	final int x[] = new int[GAME_UNITS];
	final int y[] = new int[GAME_UNITS];
	int bodyParts = 6;
	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("Hack",Font.BOLD, 75));
			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_HEIGHT / 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() {
		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(y[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 TEXT
		g.setColor(Color.RED);
		g.setFont(new Font("Hack",Font.BOLD, 75));
		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("Hack",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_LEFT :
					if(direction != 'R') {
						direction = 'L';
					}
					break;
				case KeyEvent.VK_RIGHT :
					if(direction != 'L') {
						direction = 'R';
					}
					break;
				case KeyEvent.VK_UP :
					if(direction != 'D') {
						direction = 'U';
					}
					break;
				case KeyEvent.VK_DOWN :
					if(direction != 'U') {
						direction = 'D';
					}
					break;
			}
		}
	}
}