Hit detection.

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Pacman here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Pacman extends Actor
{

    /**
     * Act - do whatever the Pacman wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */

    public Pacman()
    {
        GreenfootImage image = getImage();  
        image.scale(35, 35);
        setImage(image); 
    }

    public void act() 
    {
        controls();
        move(-3);
        eat();
        checkRightWalls();
        platformAbove();
        checkLeftWalls();
        platformBelow();
    } 

    private void controls()
    {
        if ( Greenfoot.isKeyDown("right") || Greenfoot.isKeyDown("D") ) {
            setRotation(-180);
        }
        if ( Greenfoot.isKeyDown("left") || Greenfoot.isKeyDown("A") ) {
            setRotation(-0);
        }
        if ( Greenfoot.isKeyDown("up") || Greenfoot.isKeyDown("W") ) {
            setRotation(-270);
        }
        if ( Greenfoot.isKeyDown("down") || Greenfoot.isKeyDown("S") ) {
            setRotation(-90);
        }
    } 

    private boolean platformAbove()
    {
        int spriteHeight = getImage().getHeight();
        int yDistance = (int) (spriteHeight / -2 );

        Actor ceiling = getOneObjectAtOffset(0, yDistance, Wall.class);
        if(ceiling != null)
        {

            bopHead(ceiling);
            return true;  
        }
        else
        {

            return false;
        }
    }

    public void bopHead (Actor ceiling)
    {
        int ceilingHeight = ceiling.getImage().getHeight();
        int newY = ceiling.getY() +(ceilingHeight + getImage().getWidth())/2;

        setLocation(getX() , newY);
    }

    private boolean platformBelow()
    {
        int spriteHeight = getImage().getHeight();
        int yDistance = (int) (spriteHeight / 2 );

        Actor floor = getOneObjectAtOffset(0, yDistance, Wall.class);
        if(floor != null)
        {

            bopHeads(floor);
            return true;  
        }
        else
        {

            return false;
        }
    }

    public void bopHeads (Actor floor)
    {
        int ceilingHeight = floor.getImage().getHeight();
        int newYL = floor.getY() -(ceilingHeight + getImage().getWidth())/2;

        setLocation(getX() , newYL);
    }

    private boolean checkRightWalls()
    {
        int spritewidth = getImage().getWidth();
        int xDistance = (int)(spritewidth/2);

        Actor rightwall = getOneObjectAtOffset(xDistance, 0, Wall.class);
        if(rightwall == null)
        {
            return false;  
        }
        else
        {
            stopByRightWall(rightwall);
            return true;
        }
    }

    public void stopByRightWall (Actor rightwall)
    {
        int wallWidth = rightwall.getImage().getWidth();
        int newX = rightwall.getX() -(wallWidth + getImage().getWidth())/2;

        setLocation(newX , getY());
    }

    private boolean checkLeftWalls()
    {
        int spritewidth = getImage().getWidth();
        int xDistance = (int)(spritewidth/2);

        Actor leftwall = getOneObjectAtOffset(xDistance, 0, Wall.class);
        if(leftwall == null)
        {
            return false;  
        }
        else
        {
            stopByLeftWall(leftwall);
            return true;
        }
    }

    public void stopByLeftWall (Actor leftwall)
    {
        int wallWidth = leftwall.getImage().getWidth();
        int newXL = leftwall.getX() -(wallWidth + getImage().getWidth())/2;

        setLocation(newXL , getY());
    }

    public void eat()
    {

        Actor Pellet = getOneObjectAtOffset(0, 0,Pellet.class);
        if(Pellet != null)
        {
            World world = getWorld();
            world.removeObject(Pellet);
            ((MyWorld)world).counter.add(1);
        }
    }
}

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Wall here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Wall extends Actor
{
    /**
     * Act - do whatever the Wall wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
      
    }   
    
    public Wall()
    {
       GreenfootImage image = getImage();  
        image.scale(60, 40);
        setImage(image); 
    }
}

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class MyWorld here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class MyWorld extends greenfoot.World
{
    Counter counter;
    /**
     * Constructor for objects of class MyWorld.
     * 
     */
    public MyWorld()
    {    
        // Create a new world with 600x400 cells with a cell size of 1x1 pixels.
        super(800, 600, 1); 
        prepare();
    }

    /**
     * Prepare the world for the start of the program.
     * That is: create the initial objects and add them to the world.
     */
    private void prepare()
    {
        Pacman pacman = new Pacman();
        addObject(pacman,780,100);

        counter = new Counter();
        addObject(counter,728,26);

        Wall wall = new Wall();
        addObject(wall,770,66);

        Wall wall2 = new Wall();
        addObject(wall2,710,66);

        Wall wall3 = new Wall();
        addObject(wall3,650,66);

        Wall wall4 = new Wall();
        addObject(wall4,590,66);
        
    }
}