Need some help

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
public class Mover extends Actor
{
    private static final int acceleration = 2;      // down (gravity)
    private static final int speed = 7;             // running speed (sideways)
    
    private int vSpeed = 0;                         // current vertical speed
    
    /**
     * Move a bit to the right.
     */
    public void moveRight()
    {
        setLocation ( getX() + speed, getY() );
    }
    
    /**
     * Move a bit to the left.
     */
    public void moveLeft()
    {
        setLocation ( getX() - speed, getY() );
    }
    
    /**
     * Return true if we're on firm ground that we can stand on.
     */
    public boolean onGround()
    {
        Object under = getOneObjectAtOffset(0, getImage().getHeight()/2-8, null);
        return under != null;
    }

    /**
     * Set a speed for a vertical movement. Positive values go down, negative values
     * go up.
     */
    public void setVSpeed(int speed)
    {
        vSpeed = speed;
    }
    
    /**
     * Apply gravity and fall downwards until we hit ground or the bottom of the screen.
     */
    public void fall()
    {
        setLocation ( getX(), getY() + vSpeed);
        vSpeed = vSpeed + acceleration;
        if ( atBottom() )
            gameEnd();
    }
    
    /**
     * Return true if we're at the bottom of the screen.
     */
    private boolean atBottom()
    {
        return getY() >= getWorld().getHeight() - 2;
    }
    
    /**
     * End this game (that is: stop the simuation).
     */
    private void gameEnd()
    {
        Greenfoot.stop();
    }


}

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

/**
 * the evolution animal needs to go from one side to the other
 */
public class Animal1 extends Mover
{
    private static final int jumpStrength = 16;
    private int level;
    private int jumped = 0;   // count how often we've jumped
    
    public Animal1()
    {
        level = 1;
    }
    
    public void act() 
    {
        checkKeys();        
        checkFall();
        checkNextLevel();
    }
    
    private void checkKeys()
    {
        if (Greenfoot.isKeyDown("left") )
        {
            setImage("pengu-left.png");
            moveLeft();
        }
        if (Greenfoot.isKeyDown("right") )
        {
            setImage("pengu-right.png");
            moveRight();
        }
        if (Greenfoot.isKeyDown("space") )
        {
            if (onGround())
                jump();
        }
    }    
    
    private void jump()
    {
        setVSpeed(-jumpStrength);
        fall();
        jumped++;
    }
    
    private void checkFall()
    {
        if (onGround()) {
            setVSpeed(0);
        }
        else {
            fall();
        }
    }

    /**
     * Check whether we should go to the next level, and if yes, start the next level.
     */
    private void checkNextLevel()
    {
        if (getX() == getWorld().getWidth()-1) {
            if (level == 1) {
                level = 2;
                getWorld().removeObject(this);

            }
            else {
                level = 1;
                getWorld().removeObject(this);

            }
        }
    }


}