Scrolling World

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

/**
 * CLASS:OpenScrollWorld
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class OpenScrollWorld extends Levels
{
    public static final int WIDE=1000;
    public static final int HIGH=866;
    Scroller scroller;
    Actor scrollActor;
    HealthBar healthbar = new HealthBar();
    Health_Text health_text = new Health_Text();
    static GreenfootSound music = new GreenfootSound("GameMusic.wav");
    /**
     * Constructor for objects of class ActorScrollWorld.
     * 
     */
    public OpenScrollWorld()
    {    
        GreenfootImage image=new GreenfootImage("Clowd.png");
        scroller=new Scroller(this,image);
        scroller.scroll(0,0);
        prepare();
        
    }
    
    public void act()
    {
        if(scrollActor!=null)
        {
            scroll();
        }
        else 
        {
            keyScroll();
        }
        music.play();
    }
    private void keyScroll()
    {
        int dsx=0,dsy=0;
        if(Greenfoot.isKeyDown("right"))
        {
            dsx++;
        }
        if(Greenfoot.isKeyDown("left"))
        {
            dsx--;
        }
        if(Greenfoot.isKeyDown("down"))
        {
            dsy++;
        }
        if(Greenfoot.isKeyDown("up"))
        {
            dsy--;
        }
        int rate=15;
        scroller.scroll(dsx*rate,dsy*rate);
    }
    private void scroll()
    {
        int loX=200;
        int hiX=WIDE-200;
        int loY=200;
        int hiY=HIGH-200;
        int dsx=0;
        int dsy=0;
        if(scrollActor.getX()<loX)
        {
            dsx=scrollActor.getX()-loX;
        }
        if(scrollActor.getX()>hiX)
        {
            dsx=scrollActor.getX()-hiX;
        }
        if(scrollActor.getY()<loY)
        {
            dsy=scrollActor.getY()-loY;
        }
        if(scrollActor.getY()>hiY)
        {
            dsy=scrollActor.getY()-hiY;
        }
        int rate=15;
        int signX=(int)Math.signum(dsx),signY=(int)Math.signum(dsy);
        dsx=signX*Math.min(Math.abs(dsx),rate);
        dsy=signY*Math.min(Math.abs(dsy),rate);
        scroller.scroll(dsx,dsy);
    }
}

int imageWidth = image.getWidth();
int imageHeight = image.getHeight();
scroller=new Scroller(this,image,imageWidth,imageHeight);

scroller=new Scroller(this,image,2000,600);