java.lang.NullPointerException at ScoreBoard.redraw(ScoreBoard.java:53) at ScoreBoard.decShelterCount(ScoreBoard.java:123) at Player.placeShelt(Player.java:71) at Player.act(Player.java:44) this is what i get when i press the spacebar to get a shelter

The player is not using the score board that is in the world. You have it creating and using another one which it should not do. When trying to access the score board, always use (from an Actor subclass)

ok that made the errors go away and the shelters work good now but i can only place one shelter to the world after that i press the spacebar and nothing happens public class Player extends Actor { private Shelter placeShelt= new Shelter(10); int Ammo = 10; /** * 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() { if (Greenfoot.isKeyDown("left")) { move(-1); } if (Greenfoot.isKeyDown("right")) { move(1); } if(isTouching(Lobstrosity.class) || getWorld().getObjects(Lobstrosity.class).isEmpty()) { getWorld().removeObjects(getWorld().getObjects(null)); } if (Greenfoot.isKeyDown("space") && placeShelt.getWorld() == null && placeShelt.hasHealth()) { placeShelt(); } /** * fire the PoisonBomb */ if ("b".equals(Greenfoot.getKey()) && getWorld().getObjects(PoisonBomb.class).isEmpty()) { if(Ammo>0) { PoisonBomb poisonbomb = new PoisonBomb(); getWorld().addObject(poisonbomb, getX(), getY()); Ammo--; ((MyWorld)getWorld()).getScoreBoard().decBombCount(); } else { } } } public void placeShelt() { getWorld().addObject(placeShelt, getX(), getY()-50); ((MyWorld)getWorld()).getScoreBoard().decShelterCount(); } }

this is what i have right now lobsters public class Lobstrosity extends Actor { private int touching; private int count=1; private ScoreBoard score = new ScoreBoard(); /** * Act - do whatever the Lostrosity wants to do. This method is called whenever * the 'Act' or 'Run' button gets pressed in the environment. */ public void act() { setRotation(90); move(1); if (isAtEdge()) { getWorld().addObject(new Lobstrosity(),Greenfoot.getRandomNumber(800)+1, Greenfoot.getRandomNumber(240)+40); setLocation(Greenfoot.getRandomNumber(800)+1, Greenfoot.getRandomNumber(240)+40); ((MyWorld)getWorld()).getScoreBoard().incScore(1); //((MyWorld)getWorld()).getScoreBoard().getHighScore(); if(score.getScore() > score.getHighScore()) { ((MyWorld)getWorld()).getScoreBoard(); score.setHighScore(score.getScore()); score.resetForNewGame(); } } if (isTouching(Shelter.class)==true) { ((Shelter)getOneIntersectingObject(Shelter.class)).reduceStrength(); getWorld().removeObject(this); } } Player public class Player extends Actor { private Shelter placeShelt= new Shelter(10); int Ammo = 10; int sheltersCount = 3; int initialStrength=10; private ScoreBoard score = new ScoreBoard(); /** * 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() { if (Greenfoot.isKeyDown("left")) { move(-1); } if (Greenfoot.isKeyDown("right")) { move(1); } if(isTouching(Lobstrosity.class) || getWorld().getObjects(Lobstrosity.class).isEmpty()) { getWorld().removeObjects(getWorld().getObjects(null)); if(score.getScore() > score.getHighScore()) { ((MyWorld)getWorld()).getScoreBoard(); score.setHighScore(score.getScore()); score.resetForNewGame(); } } if (Greenfoot.isKeyDown("space") && placeShelt.getWorld() == null && placeShelt.hasHealth()) { placeShelt(); } /** * fire the PoisonBomb */ if ("b".equals(Greenfoot.getKey()) && getWorld().getObjects(PoisonBomb.class).isEmpty()) { if(Ammo>0) { PoisonBomb poisonbomb = new PoisonBomb(); getWorld().addObject(poisonbomb, getX(), getY()); Ammo--; ((MyWorld)getWorld()).getScoreBoard().decBombCount(); } else { } } } public void placeShelt() { if(((MyWorld)getWorld()).getScoreBoard().getShelterCount()>0) { getWorld().addObject(placeShelt, getX(), getY()-50); ((MyWorld)getWorld()).getScoreBoard().decShelterCount(); sheltersCount--; } else { } } } myWorld public class MyWorld extends World { // YOU MAY WISH/NEED TO ADD INSTANCE VARIABLE(S) HERE!!! ScoreBoard scoreboard = new ScoreBoard(); int sheltersLeft = 3; /** * Constructor for objects of class MyWorld. */ public MyWorld() { // Create a new world with 600x400 cells with a cell size of 1x1 pixels. super(800, 600, 1); prepare(); act(); } private void prepare() { Player player = new Player(); addObject(player, 400, 575); addObject(new Lobstrosity(),400,Greenfoot.getRandomNumber(240)+40); } /** * getScoreBoard gives us the Scoreboard found in the world * NOTE ---> YOU ***MUST*** CODE THIS !!! * * @return the ScoreBoard object seen in the world */ public ScoreBoard getScoreBoard() { addObject(scoreboard,400, 10); return scoreboard; } public void act() { if (Greenfoot.isKeyDown("n") && getObjects(Lobstrosity.class).isEmpty()) { Player player = new Player(); addObject(player, 400, 575); scoreboard = new ScoreBoard(); addObject(scoreboard,400, 10); Lobstrosity lobstrosity = new Lobstrosity(); addObject(lobstrosity,400,Greenfoot.getRandomNumber(240)+40); } } /** * containsShelter tells us whether or not a shelter * is already in the world. * @return true if there is a shelter, false if not */ //public boolean containsShelter() //{ //} /** * containsBomb tells us whether or not a bomb * is already in the world. * @return true if there is a bomb, false if not */ public boolean containsBomb() { // fairly inelegant and inefficient way to code this // but avoids the need for code elsewhere. return (!getObjects(PoisonBomb.class).isEmpty()); } /** * lobstrosityCount tells us how man lobstrosities are * in the World. * @return the number of lobstrosities in the world */ public int lobstrosityCount() { return getObjects(Lobstrosity.class).size(); } } ScoreBoard public class ScoreBoard extends Actor { private int gameScore; // current game score private int highScore; // high score so far private int sheltersLeft; // number of shelters left private int bombsLeft; // number of bombs left // "global" representing the height (bottom to top) of a // ScoreBoard public static final int SCOREBOARD_HEIGHT = 25; /** * Constructor for ScoreBoard to build starting scoreboard. */ public ScoreBoard() { gameScore=0; // no game started yet, so score is 0 highScore=0; // no game started yet, so high score is 0 bombsLeft=10; // no game started yet, so all bombs available sheltersLeft=3; // no game started yet, so all shelters available } // Greenfoot trick to draw image ater object added to world. protected void addedToWorld(World toWorld) { redraw(); } // redraws scoreboard, updating values displayed as we go // we don't want this called from outside the class, so // it is private in this case. private void redraw() { // needs regular access to world, so store in a variable. MyWorld placedIn = (MyWorld) getWorld(); // check to see if image is valid. If not, rebuild it. GreenfootImage img = getImage(); if (img==null || img.getWidth()!= placedIn.getWidth() || img.getHeight()!=SCOREBOARD_HEIGHT) { img = new GreenfootImage(placedIn.getWidth(), SCOREBOARD_HEIGHT); setImage(img); } // fill image with gray background img.setColor(Color.LIGHT_GRAY); img.fill(); // draw scores, etc. in black img.setColor(Color.BLACK); img.drawString("Score:"+ gameScore, 600, SCOREBOARD_HEIGHT-8); img.drawString("High Score:"+ highScore, 400, SCOREBOARD_HEIGHT-8); // draw in shelter and bomb stats img.drawString("Shelters:"+ sheltersLeft, 100, SCOREBOARD_HEIGHT-8); img.drawString("Bombs:"+ bombsLeft, 300, SCOREBOARD_HEIGHT-8); } /** * incScore - adds something to score * @param byVal - value to add to the score. */ public void incScore(int byVal) { gameScore+=byVal; redraw(); } /** * getScore - returns the current score * @return the current game score */ public int getScore() { return gameScore; } /** * decBombCount - decrease the number of bombs by 1, but only * if there are any bombs left * @return true when there was at least 1 bomb left, * false otherwise */ public boolean decBombCount() { // if there are bombs left if (bombsLeft>0) { bombsLeft--; // reduce bomb count redraw(); // redraw image to see updated bomb count return true; // we succeeded! } return false; // not enough bombs to do this! } /** * decShelterCount - decrease the number of shelters by 1, but * only if there are any shelters left * @return true when there was at least 1 shelter left, * false otherwise */ public boolean decShelterCount() { // if there are shelters left if (sheltersLeft>0) { sheltersLeft--; // now there's one less shelter redraw(); // redraw to reflect change return true; // we had a shelter left! } return false; // no shlters left! } /** * getShelterCount returns how mny shelters are available * * @return the current number of shelters */ public int getShelterCount() { return sheltersLeft; } /** * getHighScore returns the current value of high score * * @return the current high score */ public int getHighScore() { return highScore; } /** * setHighScore gives high score a new value * * @param newScore the intended new value of high score */ public void setHighScore(int newScore) { highScore = newScore; // store the new high score redraw(); // redisplay scoreboard } /** * resetForNewGame resets the scoreboard data for a new game * * note that this does NOT reset high score */ public void resetForNewGame() { // games start with 3 shelters, 10 bombs, and a score of 0 sheltersLeft=3; bombsLeft=10; gameScore=0; redraw(); // redisplay the scoreboard. } } shelter public class Shelter extends Actor { private int strengthLeft; // remaining strength private int strength = 10; // dimensions of the shelter object. Note that these are // private as there is no reason to utiize these outside // of this class. private static final int SHELTER_WIDTH = 225; private static final int SHELTER_HEIGHT = 25; public void act() { /** * Constructor for a shelter. * * @param initialStrength is the starting strength of * this shelter */ } public boolean hasHealth() { return strengthLeft > 0; } public Shelter(int initialStrength) { strengthLeft = initialStrength; // remember initial strength redraw(); // redraw the shelter } // redraw simply rebuilds the image for the shelter. // note that methods outside this class should not call // redraw, so it is private. private void redraw() { // (re)build image if necessary GreenfootImage img = getImage(); if (img==null || img.getWidth()!=SHELTER_WIDTH || img.getHeight()!=SHELTER_HEIGHT) { img = new GreenfootImage(SHELTER_WIDTH, SHELTER_HEIGHT); setImage(img); } // set background to light gray img.setColor(Color.LIGHT_GRAY); img.fill(); // add text repressenting the strength left in black img.setColor(Color.BLACK); img.drawString(""+ strengthLeft, SHELTER_WIDTH/2-10, SHELTER_HEIGHT-8); } /** * reduceStrngth reduces this shelter's strength by 1 unit */ public void reduceStrength() { reduceStrength(1); // use the other reduceStrength method } /** * reduceStrength reduces the strength of the shelter by a * requested amount. * @param byVal is the amount to reduce this shelter's strength */ public void reduceStrength(int byVal) { strengthLeft-=byVal; // reduce the strength // if shelter is still strong enough to function ... if (strengthLeft>0) redraw(); // ... redisplay the shelter else // shelter not strong enough to function getWorld().removeObject(this); // remove this shelter } }

I would figure you would want some type of powering up for the shelter before allowing it to be put in the world again (allowing the shelter to be put back in the world again right after it loses all its strength doesn't seem right). To allow the shelter back into the world, first call: