java.lang.NullPointerException
at titan1.act(titan1.java:10)
...

ava.lang.NullPointerException
	at titan1.act(titan1.java:10)
	at greenfoot.core.Simulation.actActor(Simulation.java:567)
	at greenfoot.core.Simulation.runOneLoop(Simulation.java:530)
	at greenfoot.core.Simulation.runContent(Simulation.java:193)
	at greenfoot.core.Simulation.run(Simulation.java:183)

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

public class titan1 extends proplv1
{
    public int Score=0;

    public void act() {
        titanjatoh();
        getWorld().showText("Score: "+String.valueOf(Score), 50, 10);
        if(getWorld() != null && !getWorld().getObjects(pelurulevi.class).
        isEmpty() &&cektitan())
            kena();          

    }  

    public boolean cekjatoh(){
        Actor batas1=getOneObjectAtOffset(0, 0, batas1.class);
        return(batas1!=null);
    }

    public void  titanjatoh(){
        setLocation(getX(), getY()+1);
        Actor batas1=getOneObjectAtOffset(0, 0, batas1.class);
        if (batas1!=null){
            getWorld().removeObject(this); 
            //JOptionPane.showMessageDialog(null, "GAME OVER");
            // Greenfoot.setWorld(new Menu());
        }
    }

    public boolean cektitan(){
        Actor pelurulevi=getOneIntersectingObject(pelurulevi.class);
        return(pelurulevi!=null);
    }

    public void kena(){
        Actor pelurulevi = getOneIntersectingObject(pelurulevi.class);
        if (pelurulevi != null){

            getWorld().removeObject(pelurulevi);
            getWorld().removeObject(this); Score+=10;
            pointitan1();

        }
    }

    public void pointitan1(){
             Score++;
            Score = Score + 10;
        }
    }