I would suggest that you have Hittable objects look for Laser objects, instead of what you have here. Only thing Laser act would need to do then is move and check for world edge (greatly simplified).

Hello, I've modified the code such that once every ten mushrooms are destroyed, a flea appears on the screen, and once every fifteen are destroyed, a scorpion emerges. However, once 10 mushrooms are destroyed, I get a null pointer exception in my GameState class, and I'm not sure why. Can someone please help? Thank you. Here's the exception: java.lang.NullPointerException at Flea.<init>(Flea.java:17) at GameState.addFlea(GameState.java:66) at GameState.checkFleas(GameState.java:103) at GameState.onAct(GameState.java:118) at MyWorld.act(MyWorld.java:44) at greenfoot.core.Simulation.actWorld(Simulation.java:573) at greenfoot.core.Simulation.runOneLoop(Simulation.java:506) at greenfoot.core.Simulation.runContent(Simulation.java:193) at greenfoot.core.Simulation.run(Simulation.java:183) Here's the code for GameState class: import greenfoot.*; import java.util.List; /** * Write a description of class GameState here. * * @author (your name) * @version (a version number or a date) */ public class GameState extends State { MyWorld w = ((MyWorld)getWorld()); public int yPosition = getWorld().getHeight() * 4/5; Score j = new Score(); private int numSegments = 10; private int numToDestroyForFlea = 10; private int numToDestroyForScorpion = 15; public GameState(MyWorld w){ super(w); } public void onSet(){ MyWorld q = ((MyWorld)getWorld()); if (!q.getObjects(Score.class).isEmpty()){ Score txt = q.getObjects(Score.class).get(0); q.setScore(q.getScore() - q.getScore()); txt.setText("Score: " + q.getScore()); } q.setLvl(1); w.setGameOver(false); Player player = new Player(); getWorld().addObject(player, getWorld().getWidth()/2, getWorld().getHeight() - player.getImage().getHeight()/2); Spider s = new Spider(); getWorld().addObject(s, s.getImage().getWidth()/2, getWorld().getHeight() - s.getImage().getHeight()/2); for (int i = 0; i < 10; i++){ Centipede centipede = new Centipede(); getWorld().addObject(centipede, getWorld().getWidth()/2 - centipede.getImage().getWidth() * i, centipede.getImage().getHeight()/2); } for (int i = 0; i < 42; i++){ int x = Greenfoot.getRandomNumber(getWorld().getWidth()); int y = Greenfoot.getRandomNumber(getWorld().getHeight()); Mushroom mushroom = new Mushroom(); if (getWorld().getObjectsAt(x, y, Mushroom.class).size() == 0 && (y >= 20 && y <= getWorld().getHeight() - player.getImage().getHeight())){ getWorld().addObject(mushroom, x, y); mushroom.goToGrid(); } } j.setText(w.getScore()); j.setSize(MyWorld.GRIDSIZE); j.setOutLColor(null); getWorld().addObject(j, j.getImage().getWidth(), j.getImage().getHeight()/2); } public void addFlea(){ for (int i = 0; i < 1; i++){ Flea f = new Flea(); getWorld().addObject(f, Greenfoot.getRandomNumber(getWorld().getWidth()), -f.getImage().getHeight()); } } public void addScorpion(){ for (int i = 0; i < 1; i++){ if (w.getLvl() >= 1 && w.getLvl() <= 3){ Scorpion sco = new Scorpion(); getWorld().addObject(sco, 0, Greenfoot.getRandomNumber(getWorld().getHeight()/3)); } if (w.getLvl() > 3 && w.getLvl() < 7){ Arachnoid a = new Arachnoid(); getWorld().addObject(a, 0, Greenfoot.getRandomNumber(getWorld().getHeight()/4)); } } } public void snapAllToGrid(){ List<Mushroom> plant = getWorld().getObjects(Mushroom.class); for (int i = 0; i < plant.size(); i++){ Mushroom fungi = plant.get(i); fungi.goToGrid(); } } public void onRemove(){ // Remove anything when state is changed List <Actor> all = getWorld().getObjects(Actor.class); getWorld().removeObjects(all); } public void checkFleas(){ if (w.getDestroyed() == numToDestroyForFlea){ numToDestroyForFlea += 10; addFlea(); } } public void checkScorpions(){ if (w.getDestroyed() == numToDestroyForScorpion){ numToDestroyForScorpion += 15; addScorpion(); } } public void onAct(){ // Do what happpens in the state. Check if needs to be changed if (getWorld() != null){ checkFleas(); checkScorpions(); } if (getWorld().getObjects(Centipede.class).isEmpty()){ Greenfoot.delay(15); w.setLvl(w.getLvl() + 1); for (int i = 0; i < 10; i++){ Centipede centipede = new Centipede(); //centipede.setDx(centipede.getDx() + 1); getWorld().addObject(centipede, getWorld().getWidth()/2 - centipede.getImage().getWidth() * i, centipede.getImage().getHeight()/2); } Centipede c = new Centipede(); getWorld().addObject(c, getWorld().getWidth() - c.getImage().getWidth() * 2, c.getImage().getHeight()/2); List<Mushroom> cacti = getWorld().getObjects(Mushroom.class); for (int i = 0; i < cacti.size(); i++){ Mushroom food = cacti.get(i); food.getImage().setTransparency(255); food.goToGrid(); } Spider s = new Spider(); getWorld().addObject(s, s.getImage().getWidth()/2, getWorld().getHeight() - s.getImage().getHeight()/2); if (getWorld() != null){ checkFleas(); checkScorpions(); } } if (getWorld().getGameOver() == true){ getWorld().setState(new GameOverState(getWorld())); } } }

Here's the code for the Flea class: import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo) /** * Write a description of class Flea here. * * @author (your name) * @version (a version number or a date) */ public class Flea extends Hittable { boolean isRemoved = false; int dy = 3; public Flea(){ getImage().scale(MyWorld.GRIDSIZE, MyWorld.GRIDSIZE); } MyWorld b = (MyWorld) getWorld(); Score scTxt = b.getObjects(Score.class).get(0); /** * Act - do whatever the Flea wants to do. This method is called whenever * the 'Act' or 'Run' button gets pressed in the environment. */ public void act() { // Add your action code here. Score scTxt = b.getObjects(Score.class).get(0); if (b.getPaused() == false){ setLocation(getX(), getY() + dy); if (isTouching(Player.class)){ MyWorld w = ((MyWorld)getWorld()); w.setGameOver(true); } if (Greenfoot.getRandomNumber(100) == 20){ Mushroom m = new Mushroom(); getWorld().addObject(m, getX(), getY()); m.goToGrid(); } /*if (getY() > getWorld().getHeight()){ getWorld().removeObject(this); }*/ if (isTouching(Laser.class)){ removeTouching(Laser.class); onHit(); } } } public void onHit(){ Mushroom a = new Mushroom(); getWorld().addObject(a, getX(), getY()); a.goToGrid(); destroy(); b.setScore(b.getScore() + 100); scTxt.setText("Score: " + b.getScore()); } } Thanks!

You cannot get the Score object from the world in the constructor of the Flea class. The constructor is executed during the creation of the Flea object -- before it can be placed into any world. Override the Actor class addedToWorld(World) method to get the Score object. As an alternative, you could pass the Score object by way of a parameter argument to the Flea constructor.

Upon a second look, I see that the errant code is not actually in the constructor of the class; however, it is still processed during object creation. Only declare the b and scTxt fields where you have them. Do not assign them their values there. Those assignments cannot be performed before the actor is in a world. You have this: Change lines 4 and 5 to: Then remove line 9. Finally, add the following method to the class: You could also remove line 13 and change the 'w' to 'b' in line 14. All occurrences of 'getWorld()' or '(MyWorld)getWorld()' can also be replaced with 'b'.

Hi, I'm trying to make the player move in conjunction with the mouse moving. The player shouldn't be able to cross the y-position of 4/5 of world height (he's restricted to the bottom-fifth). However, I'm having trouble doing this. I read the API, but I don't really understand how to use it in my code. Can someone please help? Thank you. Here's the code for my Player class: import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo) //import java.lang.String; /** * Write a description of class Player here. * * @author (your name) * @version (a version number or a date) */ public class Player extends Actor { private int numPresses = 0; public Player(){ getImage().scale(MyWorld.GRIDSIZE * 3/2, MyWorld.GRIDSIZE * 3/2); } int dx = 2; int dy = -2; /** * Act - do whatever the Player wants to do. This method is called whenever * the 'Act' or 'Run' button gets pressed in the environment. */ public void act() { // Add your action code here. MyWorld v = (MyWorld)getWorld(); if (v.getPaused() == false){ move(); if (Greenfoot.mouseClicked(this)){ Laser l = new Laser(); if (getWorld().getObjects(Laser.class).size() == 0){ getWorld().addObject(l, getX(), getY() - l.getImage().getHeight()/2); Greenfoot.playSound("LaserBeam.wav"); } } } } public void move(){ int height = getWorld().getHeight(); int width = getWorld().getWidth(); int playerW = getImage().getWidth(); int playerH = getImage().getHeight(); MouseInfo mi = Greenfoot.getMouseInfo(); if (mi != null){ if (getY() - playerH/2 > height * 4/5){ setLocation(mi.getX(), mi.getY()); } } } public int getPresses(){ return numPresses; } }

Change 'getY()' in line ??? (in the if condition in the move method) to 'mi.getY()'. (Use code tags in the future, please.)

Hi, I've added a new subclass, PointsLaser, that when used, increases the points obtained when destroying an enemy. However, I get an illiegal state exception upon shooting a centipede with a regular laser. Can someone please help? Thank you. Here's the code for my Centipede class: And here's the error: java.lang.IllegalStateException: Actor not in world. An attempt was made to use the actor's location while it is not in the world. Either it has not yet been inserted, or it has been removed. at greenfoot.Actor.failIfNotInWorld(Actor.java:714) at greenfoot.Actor.getOneIntersectingObject(Actor.java:965) at Centipede.act(Centipede.java:95) 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)