Score

public void act()
{
    fireBallHit();
    if (getWorld() == null) return; // insert this line
    minionHit();
    // etc.

((Platform)getWorld()).addPoints();

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
import javax.swing.JOptionPane;
/**
 * Write a description of class Alien here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Alien extends Actor
{
    private GreenfootImage run1 = new GreenfootImage("AlienRun1.png");
    private GreenfootImage run2 = new GreenfootImage("AlienRun2.png");
    private GreenfootImage run3 = new GreenfootImage("AlienRun3.png");
    private GreenfootImage run4 = new GreenfootImage("AlienRun4.png");
    private GreenfootImage run5 = new GreenfootImage("AlienRun5.png");
    private GreenfootImage run6 = new GreenfootImage("AlienRun6.png");
    private GreenfootImage run7 = new GreenfootImage("AlienRun7.png");
    private GreenfootImage run8 = new GreenfootImage("AlienRun8.png");
    private int frame = 1;
    private int score;
   
    private ScoreKeeper scoreKeeper;
    private double animationCounter = 1;
    /**
     * Act - do whatever the Alien wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
        
        fireBallHit();
        if (getWorld() == null)
        return;
        minionHit();
        soldierHit();
        if (Greenfoot.getRandomNumber(100) < 10)
        {
            move(-Greenfoot.getRandomNumber(50));
        }
        if(animationCounter % 4 == 0)
        animateRun();
        
        animationCounter++;
    }    
    public void animateRun()
    {
        if(frame == 1)
        {
            setImage(run1);
            
        }
        else if(frame == 2)
        {
            setImage(run2);
           
        }
        else if(frame == 3)
        {
            setImage(run3);
            
        }
        else if(frame == 4)
        {
            setImage(run4);
            
        }
        else if(frame == 5)
        {
            setImage(run5);
            
        }
        else if(frame == 6)
        {
            setImage(run6);
            
            
        }
        else if(frame == 7)
        {
            setImage(run7);
        
        }
        else if(frame == 8)
        {
            setImage(run8);
            frame = 1;
            return;
        
        }
    
        frame++;
  }
 private boolean hasTakenAHit;
  public void fireBallHit()
    {
        Actor b = getOneIntersectingObject(FireBall.class);
        if(b != null)
        {
            getWorld().removeObject(b);
            if(hasTakenAHit)
            getWorld().removeObject(this);
            hasTakenAHit = true;
            ((Platform)getWorld()).addPoint();
            
        }
        
}

 public void  minionHit()
    {
        Actor m = getOneIntersectingObject(Minion.class);
        if(m != null)
        {
            getWorld().removeObject(m);
            if(hasTakenAHit)
            getWorld().removeObject(this);
            hasTakenAHit = true;
            ((Platform)getWorld()).addPoint();
            
            
        }
      
}
public void soldierHit()
{
    Actor s = getOneIntersectingObject(Soldier.class);
    if(s != null)
    {
        JOptionPane.showMessageDialog(null, "Game Over!");
        Greenfoot.stop();
}
}
}