leveling up

/**
 * A world for the boids.
 * 
 * @author Poul Henriksen 
 * @version 2.0
 */
public class Sky extends World
{
    /**
     * Counter Object Used to keep the score
     */
    private ScoreBoard;
    private Counter scoreCounter;
    private Timer gameTimer;
    private int numberOfBoids;
    private double percentageToWin;
    private int level = 1;
    /**
     * ADD CODE HERE
     * You need a variable to keep track of what level you are on.
     */
    
    
    /**
     * Constructor for objects of class Sky.
     * 
     */
    public Sky()
    {    
        /**
         * EDIT CODE
         * Sort your code, move the "stuff" that changes to your level up method
         * The "stuff" that stays the same can stay in the constructor
         */
        
        super(800, 600, 1);
        getBackground().setColor(new Color(220,220,100));
        getBackground().fill();
        // Create a new scoreCounter object and then add it to the world
        scoreCounter = new Counter("Score: ");
        addObject(scoreCounter, 55, 580);
        ScoreBoard = new ScoreBoard("levelUp: ");
        
        /**
          * ADD CODE HERE
          * Call your level up method
          */
         levelUp();
    }
    
    /**
     * This is your level up method
     */
    public void levelUp()
    {
        /**
         * ADD CODE HERE
         * If you are not on level one, then show a scoreboard that says you have leveled up
         * Leave it on the screen for 60 time steps
         */
        if(level!=1)
        {         
            addObject(new ScoreBoard(scoreCounter.getValue()), getWidth()/2, getHeight()/2);
            Greenfoot.delay(60);
            removeObtect(ScoreBoard);
        }
        
        /**
          * ADD CODE HERE
          * Once you scoreboard goes away, you need to clear the world of all objects
          */
         Greenfoot.delay(120);
        removeObject(gameTimer);
        removeObjects(getObjects(Boid.class));
        removeObjects(getObjects(Tree.class));
        removeObjects(getObjects(Hunter.class));
         /**
          * ADD CODE HERE
          * All of the "stuff" that changes goes here
          */
         
        /**
         * Create a new timer object and then add it to the world
         */
        gameTimer = new Timer("Time Remaining: ");
        addObject(gameTimer, 100, 560);
         /**
         * Set the number of boids and the percentage to win the game
         */
        numberOfBoids = 50;
        percentageToWin = 0.25;
        populateTrees(100);
        populateBoids(numberOfBoids);
        /**
         * Create a shooter
         */
        Hunter myHunter = new Hunter();
        addObject(myHunter, getWidth()/2 ,getHeight()/2);
        /**
         * Make a predator and add it to the world
         */
        Predator myPredator = new Predator();
        addObject(myPredator, 0 , 0); 
         
         /**
          * ADD CODE HERE
          * Now that you have done everything, don't forget to add 1 to your level
          */
        
        level++;
    }