GamePanel.java

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;
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_HEIGHT*SCREEN_WIDTH)/UNIT_SIZE;
    static final int DELAY =20;
    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_HEIGHT,SCREEN_WIDTH));
        this.setFocusable(true);
        this.setBackground(Color.black);
        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(Color.orange);
                g.fillRect(x[i], y[i], UNIT_SIZE, UNIT_SIZE);
            }
        }
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free", Font.BOLD, 45));
        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 head collides with body
        for(int i=bodyParts;i>0;i--)
        {
            if((x[0]==x[i]) && (y[0]==y[i]))
            {
                running=false;
            }
        }
        // checks collision for left border
        if(x[0]<0)
        {
            running=false;
        }
        //checks collison for right border
        if(x[0]>SCREEN_WIDTH)
        {
            running=false;
        }
        // checks collision for upper border
        if(y[0]<0)
        {
            running = false;
        }
        //checks collision for lower border
        if(y[0]> SCREEN_HEIGHT)
        {
            running =false;
        }
        if(! running)
        {
            timer.stop();
        }


    }

    public void gameOver(Graphics g){
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free",Font.BOLD,75));
        FontMetrics metrics1 =getFontMetrics(g.getFont());
        g.drawString("Game Over", (SCREEN_WIDTH-metrics1.stringWidth("Game OVer"))/2, SCREEN_HEIGHT/2);
        g.setColor(Color.red);
        g.setFont(new Font("Ink Free", Font.BOLD, 45));
        FontMetrics metrics2 = getFontMetrics(g.getFont());
        g.drawString("SCORE " + applesEaten, (SCREEN_WIDTH - metrics2.stringWidth("SCORE " + applesEaten)) / 2,
                g.getFont().getSize());

    }

    
    
    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;
            }

        }

    }

    
}