GamePanel.java

package Snake;

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


import javax.swing.JPanel;


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_HEIGHT*SCREEN_WIDTH)/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){//head of the snake
                    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 checkCollision(){
        //checks if head collides with body
        for(int i = bodyParts; i>0;i--){
            if((x[0]==x[0]) && (y[0]==y[i])){
                running = false;
            }
        }
        //checks if head touches left border
        if(x[0] < 0){
            running = false;
        }
        //checks if head touches right border
        if(x[0] > SCREEN_WIDTH){
            running = false;
        }
        //checks if head touches top border
        if(y[0] < 0){
            running = false;
        }
        //checks 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) {
        // TODO Auto-generated method stub
        if(running){
            move();
            checkApple();
            checkCollision();
        }
        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;
            }
        }
    }
    
}