import greenfoot.*; 
public class Startmenu extends World
{
    public Startmenu()
    {    
        // Create a new world with 15x10 cells with a cell size of 64x64 pixels.
        super(15, 10, 64); 
        
        Start start = new Start();
        
        addObject(start,7,4);
          
        Greenfoot.setSpeed(200);
        Greenfoot.start();
    }
}

import greenfoot.*;
public class Start extends Buttons
{
    public void act() 
    {
        SwitchScreen();
    }  
    Counter counter = new Counter();
    Rocket rocket = new Rocket();
    
    private void SwitchScreen(){
        Space space = new Space();
        if(Greenfoot.mouseClicked(this)){
            counter.score=0;
            
            rocket.resetHealth();
            rocket.resetStar();
            
            Greenfoot.setSpeed(37);
            Greenfoot.setWorld(space);
}
}
}

import greenfoot.*;

public class Space extends World
{
    
    Counter counter = new Counter();
    Rocket rocket = new Rocket();
    
    public Space()
    {    
        super(15, 10, 64); 
        
        Rocket rocket = new Rocket();
        
        addObject(rocket,7,9);
        addObject(counter,1,0);
    }
    
    public void act(){
        respawn(); pause(); SpawnRandom(); getRocket();
}

public Rocket getRocket(){
    return rocket;
}

public void respawn(){
    Rocket r = new Rocket();
    getObjects(Rocket.class).size();
    if(getObjects(Rocket.class).size()==0){
        if(Greenfoot.isKeyDown("R")){
            addObject(r,7,9);}
}
}

public void pause(){ 
    if(Greenfoot.isKeyDown("P")){
        Greenfoot.stop();
    }
}

    public void SpawnRandom(){                 
        Block block= new Block();
        UFO u = new UFO();
        Repair r = new Repair();
        Star s = new Star();

        int RandomX = Greenfoot.getRandomNumber(15);
        int RandomY = Greenfoot.getRandomNumber(5);
        if(getObjects(Block.class).size() < 4){  
            if(Greenfoot.getRandomNumber(100)<10){          
    addObject(block,RandomX,RandomY);}          
}

if(getObjects(UFO.class).size() < 4){            
    if(Greenfoot.getRandomNumber(100)<10){                 
       addObject(u,RandomX,RandomY);}             
}

if(getObjects(Repair.class).size() < 2){         
   if(Greenfoot.getRandomNumber(600) == 10){               
      addObject(r,RandomX,RandomY);}               
}
    
if(rocket.starcounter == 0){                                       
   if(Greenfoot.getRandomNumber(1500) == 10){          
     addObject(s,RandomX,RandomY);}                 }
}
}

Greenfoot.setWorld(new Space());

public void respawn()
{
    if (getObjects(Rocket.class).isEmpty() && Greenfoot.isKeyDown("r"))
    {
        rocket = new Rocket();
        addObject(rocket, 7, 9);
    }
}