Changing worlds

import greenfoot.*;
public class MiniTaihei extends greenfoot.Actor 
{
    int nx = 0, ny = 0, fx = 0, fy = 0;
    Timer actTimer = new Timer(40);
    private boolean once = false;
    private boolean run = false;
    public MiniTaihei()
    {
        getImage().scale(30, 30);
    }

    public void act()
    {
        if (actTimer.iterating()) return;
        if(Wall.class == null)
        {
            if (Greenfoot.isKeyDown("a")&&(getOneObjectAtOffset(fx - 1, fy, Wall.class) == null))
            {fx--;}
            if (Greenfoot.isKeyDown("d")&&(getOneObjectAtOffset(fx + 1, fy, Wall.class) == null))
            {fx++;}
            if (Greenfoot.isKeyDown("w")&&(getOneObjectAtOffset(fx, fy - 1, Wall.class) == null))
            {fy--;}
            if (Greenfoot.isKeyDown("s")&&(getOneObjectAtOffset(fx, fy + 1, Wall.class) == null))
            {fy++;}
            if (fx*fy == 0 && fx+fy != 0) 
            {
                nx = fx;
                ny = fy;
                setLocation(getX()+nx, getY()+ny);
                actTimer.start();
            }
        }
        else if (isTouching(MiniKirie.class))
        {
            getWorld().removeObjects(getWorld().getObjects(Actor.class));
        }
    }   
}

import greenfoot.*;
public class MyWorld extends World
{
    // fields usually (by convention) go first
    
    //For GIF background stuff
    GifImage gifImg = new GifImage("Umaru.gif");
    
    //For Timing stuff
    private Actor TimeDisplay = new SimpleActor(), Cooldown = new SimpleActor();
    private int frames;
    private int Cframes = (3+Greenfoot.getRandomNumber(5))*55;
    
    //For Yen stuff
    public float AYen; //precise
    public int DYen; //rounded
    public Yen YenDisplay = new Yen();
    public int getHeight = 552 ;
    public int getWidth = 1200 ;
    
    //For Buttons stuff
    public Actor MKButton = new SimpleActor(), HButton = new SimpleActor(), BButton = new SimpleActor(), AButton = new SimpleActor(), SButton = new SimpleActor(), KButton = new SimpleActor(), EButton = new SimpleActor(), TButton = new SimpleActor();
    public Actor Buttons[] = {MKButton, HButton, BButton, AButton, SButton, KButton, EButton, TButton};
    private String ButtonImages[] = {"MKButton", "HButton", "BButton", "AButton", "SButton", "KButton", "EButton", "TButton"};
    private int ButtonsArraySize = Buttons.length;
    
    //For PIP stuff
    PIP pip;
    World minor;
    public Boolean setActiveState = false;
    Actor mouseActor; // holds the actor being dragged
    int mouseOffX, mouseOffY; // holds the offsets of mouse location from center of object being dragged
    
    // class constructors usually (by convention) go next
    
    //To construct MyWorld
    public MyWorld()
    {
        //For building the world window size
        super(1400, 675, 1);
        
        //For updating the Yen Display
        adjustYen(0); // to initialize image
        prepare();
        addObject(YenDisplay, 1265, 50); // wherever
        
        //For updating the time display
        updateTimeDisplay();
        addObject(TimeDisplay, 1265, 20);
        
        //For triggering the minigame
        updateCooldownDisplay();
        addObject(Cooldown, 1265, 35);
        
        //For adding in the buttons to add the actors into the world
        for( int i = 0; i < ButtonsArraySize; i++)
        {
            Buttons[i].setImage(ButtonImages[i] + ".png"); Buttons[i].getImage().scale(70, 70); addObject(Buttons[i], 1175, (120 + (i*50)));
            i++;
            Buttons[i].setImage(ButtonImages[i] + ".png"); Buttons[i].getImage().scale(70, 70); addObject(Buttons[i], 1325, (120 + ((i-1)*50)));
        }
    }
    
    //For GIF background
    private void gifAnimation()
    {
        for (Object obj : gifImg.getImages()) ((GreenfootImage)obj).scale(getWidth(), getHeight());
        setBackground(gifImg.getCurrentImage());
    }     
    
    // methods (by convention) go last
    
    //For executing all preccesses in MyWorld
    public void act()
    {
        
        //For GIF background
        gifAnimation();
        
        //For buying the Characters
        if(Greenfoot.mouseClicked(MKButton) && AYen >= 100 && (getObjects(MgrKanau.class).isEmpty())) {AYen -= 100; addObject(new MgrKanau(), 600, 600);}
        if(Greenfoot.mouseClicked(HButton) && AYen >= 200 && (getObjects(Hikari.class).isEmpty())) {AYen -= 200; addObject(new Hikari(), 600, 600);}
        if(Greenfoot.mouseClicked(AButton) && AYen >= 400 && (getObjects(Alex.class).isEmpty())) {AYen -= 400; addObject(new Alex(), 600, 600);}
        if(Greenfoot.mouseClicked(SButton) && AYen >= 800 && (getObjects(Sylphynford.class).isEmpty())) {AYen -= 800; addObject(new Sylphynford(), 600, 600);}
        if(Greenfoot.mouseClicked(BButton) && AYen >= 1600 && (getObjects(Bomba.class).isEmpty())) {AYen -= 1600; addObject(new Bomba(), 600, 600);}
        if(Greenfoot.mouseClicked(KButton) && AYen >= 3200 && (getObjects(Kirie.class).isEmpty())) {AYen -= 3200; addObject(new Kirie(), 600, 600);}
        if(Greenfoot.mouseClicked(EButton) && AYen >= 6400 && (getObjects(Ebina.class).isEmpty())) {AYen -= 6400; addObject(new Ebina(), 600, 600);}
        if(Greenfoot.mouseClicked(TButton) && AYen >= 12800 && (getObjects(Taihei.class).isEmpty())) {AYen -= 12800; addObject(new Taihei(), 600, 600);}
        
        //For updating the Timing stuff
        if ((++frames)%55 == 0) updateTimeDisplay();
        if ((--Cframes)%55 == 0) updateCooldownDisplay();
        if (Cframes == 0)
        {
            Minigame();
            Cframes += ((3+Greenfoot.getRandomNumber(5))*55); //chooses a cooldown time between 3-7 minutes randomly     
        }
        
        // control dragging of PIP objects
        if (Greenfoot.mousePressed(null) && mouseActor == null)
        {
            MouseInfo mouse = Greenfoot.getMouseInfo();
            if (mouse.getActor() == null || mouse.getActor().getClass() != PIP.class) return;
            mouseActor = mouse.getActor();
            mouseOffX = mouseActor.getX()-mouse.getX();
            mouseOffY = mouseActor.getY()-mouse.getY();
            removeObject(mouseActor);
            addObject(mouseActor, mouse.getX()+mouseOffX, mouse.getY()+mouseOffY);
        }
        if (mouseActor != null && Greenfoot.mouseDragged(mouseActor))
        {
            MouseInfo mouse = Greenfoot.getMouseInfo();
            mouseActor.setLocation(mouse.getX()+mouseOffX, mouse.getY()+mouseOffY);
        }
        if (mouseActor != null && Greenfoot.mouseClicked(mouseActor)) mouseActor = null;
        
        //for removing ended Minigames
        if (pip != null && pip.getWorld() == this && minor.getObjects(null).isEmpty())
        {
            removeObject(pip);
        }
    }
    
    
    //For Yen Display stuff
    public int getAccumulatedYen()
    {
        return DYen;
    }
    public void adjustYen(float adjustment)
    {
        AYen += adjustment;
        DYen = (int) AYen;
        YenDisplay.setImage(new GreenfootImage("Yen: "+DYen+"¥", 20, Color.BLACK, new Color(0, 0, 0, 0)));
    }

    //For Time Display stuff
    private void updateTimeDisplay()
    {
        int Time = frames/55; // total seconds
        int TotalMinutes = Time/60; // total minutes
        String hours = "0"+(TotalMinutes/60); // string total hours
        String minutes = "0"+(TotalMinutes%60); // string remaining minutes
        String seconds = "0"+(Time%60); // string remaining seconds
        String hrs = hours.substring(hours.length()-2); // hour output string
        String mins = minutes.substring(minutes.length()-2); // minutes output string
        String secs = seconds.substring(seconds.length()-2); // seconds output string
        String TimeFormat = "Time: "+hrs+"hrs "+mins+"mins "+secs+"secs"; //Preview: Time: 12345hrs 12mins 12secs
        TimeDisplay.setImage(new GreenfootImage(TimeFormat, 20, Color.BLACK, new Color(0, 0, 0, 0)));
        
    }
    
    //Minigame stuff
    
    //For timing the appearance of the Minigame
    private void updateCooldownDisplay()
    {
        int Time = Cframes/55;
        String minutes = "0"+(Time/60); // string remaining minutes
        String seconds = "0"+(Time%60); // string remaining seconds
        String mins = minutes.substring(minutes.length()-2); // minutes output string
        String secs = seconds.substring(seconds.length()-2); // seconds output string
        String TimeFormat = "Minigame countdown: "+mins+"mins "+secs+"secs"; //Preview: Time: 12345hrs 12mins 12secs
        Cooldown.setImage(new GreenfootImage(TimeFormat, 20, Color.BLACK, new Color(0, 0, 0, 0)));
    }
    
    //For choosing and calling out the Minigame
    private void Minigame()
    {
        if (pip != null && pip.getWorld() != null) return; // will not add new pip if one is already in world
        minor = null;
        switch (Greenfoot.getRandomNumber(3))
        {
            case 0: if (!getObjects(Taihei.class).isEmpty()) minor = new Minigame1(); break;
            case 1: if (!getObjects(Sylphynford.class).isEmpty()) minor = new Minigame2(); break;
            case 2: if (!getObjects(Ebina.class).isEmpty()) minor = new Minigame3(); break;
            case 3: if (!getObjects(Alex.class).isEmpty()) minor = new Minigame4(); break;
            case 4: if (!getObjects(Bomba.class).isEmpty()) minor = new Minigame5(); break;
        }
        if (minor != null)
        {
            pip = new PIP(minor, new Class[] {});
            pip.setActiveState(true);
            addObject(pip, 690, 110);
        }
    }
    private void prepare()
    {
        addObject(new Umaru(), 700, 338);
    }
}

public class Timer  
{
    private int delayAmount; // the number of steps to complete one cycle
    private int counter; // the current value of the timer
    private boolean paused; // the current paused state of the timer
    private boolean looping; // the looping state of the timer
    
    /**
     * this secondary constructor creates a timer object that does not loop automatically
     *
     * @param amount the number of steps to complete one cycle
     */
    public Timer(int amount)
    {
        this(amount, false); // calls the primary constructor with a looping value of false
    }
    
    /**
     * this primary constructor sets up a timer object
     *
     * @param amount the number of steps to complete one cycle
     * @param toLoop a flag indicating whether the timer should loop automatically or not
     */
    public Timer(int amount, boolean toLoop)
    {
        delayAmount = amount; // number of steps to delay
        looping = toLoop; // save looping state
        if (looping) counter = -1; // adjust counter if looping (looping counters must be explicitly started)
    }
    
    /**
     * usually called by the object that created the timer to execute one step and return a boolean value
     * indicating whether the timer is still running or not; a paused state is a busy state and returns a
     * true value just as if the timer was still running
     *
     * @return a boolean value indicating whether the timer is paused or has not completed a cycle, or not
     */
    public boolean iterating()
    {
        if (paused) return true; // timer is paused
        if (counter == 0 && looping) counter = delayAmount; // reset counter if end of cycle and looping
        if (counter > 0) counter--; // decrement counter
        return counter > 0; // return true if cycle is not complete
    }
    
    /**
     * stops the timer
     */
    public void stop()
    {
        counter = -1; // sets counter value to one indicating the timer is stopped
        paused = true; // sets paused flag to true
    }
    
    /**
     * starts the timer
     */
    public void start()
    {
        paused = false; // sets pausd flag to false
        counter = looping ? 0 : delayAmount; // sets counter to an appropriate value depending on looping state
    }
    
    /**
     * un-pauses the timer
     */
    public void resume()
    {
        paused = false; // sets paused flag to false
    }
    
    /**
     * pauses the timer
     */
    public void pause()
    {
        paused = true; // sets paused flag to true
    }
}

actTimer = new Timer(40);

if (fx*fy == 0 && fx+fy != 0 && getOneObjectAtOffset(fx, fy, Wall.class) == null)

int fx = 0, fy = 0;