试图通过setter和getter增加值，但是值不会增加？

Question

In my assingment, I'm supposed to modify a greenfoot project to display the values of viruses and bacteria touched and missed in the game by creating private data types and using setters and getters to demonstrate understanding of data encapsulation, as well as modify the scoring system. I was able to get the scoring system to work, but when I run the game, it will only increment the values of setters by one and won't count passed that.

 public class Bloodstream extends World
{
    private int score;
    private int time;

    /**New Private variables **/

    private int numberOfBacteriaTouched;
    private int numberOfBacteriaMissed;
    private int numberOfVirusTouched;
    private int numberOfVirusMissed;

    /**
     * Constructor: Set up the staring objects.
     */
    public Bloodstream()
    {    
        super(780, 360, 1); 
        setPaintOrder(Border.class);
        prepare();
        score = 0;
        time = 2000;
        this.numberOfBacteriaTouched= 0;
        this.numberOfBacteriaMissed = numberOfBacteriaMissed;
        this.numberOfVirusTouched = 0;
        this.numberOfVirusMissed = numberOfVirusMissed;
        showScore();
        showTime();
    }

    /**
     * Create new floating objects at irregular intervals.
     */
    public void act()
    {
        if (Greenfoot.getRandomNumber(100) < 3)
        {
            addObject(new Bacteria(), 779, Greenfoot.getRandomNumber(360));
        }

        if (Greenfoot.getRandomNumber(100) < 1)
        {
            addObject(new Lining(), 779, 0);
        }

        if (Greenfoot.getRandomNumber(100) < 1)
        {
            addObject(new Lining(), 779, 359);
        }

        if (Greenfoot.getRandomNumber(100) < 1)
        {
            addObject(new Virus(), 779, Greenfoot.getRandomNumber(360));
        }

        if (Greenfoot.getRandomNumber(100) < 6)
        {
            addObject(new RedCell(), 779, Greenfoot.getRandomNumber(360));
        }
        countTime();
    }

    /** Getters for new variables **/

    public int getNumberOfBacteriaTouched()
    {
        return numberOfBacteriaTouched;
    }

    public int getNumberBacteriaMissed()
    {
        return numberOfBacteriaMissed;
    }

    public int getNumberOfVirusTouched()
    {
        return numberOfVirusTouched;
    }

    public int getNumberOfVirusMissed()
    {
        return numberOfVirusMissed;
    }

        /** Setters for new variables **/

    public void setNumberOfBacteriaTouched(int numberOfBacteriaTouched)
    {
        this.numberOfBacteriaTouched = numberOfBacteriaTouched;
    }

    public void setNumberOfBacteriaMissed(int numberOfBacteriaMissed)
    {
        this.numberOfBacteriaMissed= numberOfBacteriaMissed;
    }

    public void setNumberOfVirusTouched(int numberOfVirusTouched)
    {
        this.numberOfVirusTouched= numberOfVirusTouched;
    }

    public void setNumberOfVirusMissed(int numberOfVirusMissed)
    {
        this.numberOfVirusMissed= numberOfVirusMissed;
    }


    /**
     * Add some points to our current score. (May be negative.)
     * If the score falls below 0, game's up.
     */
    public void addScore(int points)
    {
        score = score + points;
        showScore();
        if (score < 0) 
        {
            Greenfoot.playSound("game-over.wav");
            Greenfoot.stop();
        }
    }

    /**
     * Show our current score on screen.
     */
    private void showScore()
    {
        showText("Score: " + score, 80, 25);
        showText("Bacteria Eaten: " + getNumberOfBacteriaTouched(), 80, 325);
        showText("Virus Missed: " + getNumberOfVirusMissed(), 80, 300);
    }

    /**
     * Count down the game time and display it. Stop the game 
     * with a winning message when time is up.
     */
    private void countTime()
    {
        time--;
        showTime();
        if (time == 0)
        {
            showEndMessage();
            Greenfoot.stop();
        }
    }

    /**
     * Show the remaining game time on screen.
     */
    private void showTime()
    {
        showText("Time: " + time, 700, 25);
    }

    /**
     * Show the end-of-game message on screen.
     */
    private void showEndMessage()
    {
        showText("Time is up - you win!", 390, 150);
        showText("Your final score: " + score + " points", 390, 170);
    }

    /**
     * Prepare the world for the start of the program. In this case: Create
     * a white blood cell and the lining at the edge of the blood stream.
     */
    private void prepare()
    {
        WhiteCell whitecell = new WhiteCell();
        addObject(whitecell, 128, 179);

        Lining lining = new Lining();
        addObject(lining, 126, 1);
        Lining lining2 = new Lining();
        addObject(lining2, 342, 5);
        Lining lining3 = new Lining();
        addObject(lining3, 589, 2);
        Lining lining4 = new Lining();
        addObject(lining4, 695, 5);
        Lining lining5 = new Lining();
        addObject(lining5, 114, 359);
        Lining lining6 = new Lining();
        Lining lining7 = new Lining();
        addObject(lining7, 295, 353);
        Lining lining8 = new Lining();
        Lining lining9 = new Lining();
        Lining lining10 = new Lining();
        addObject(lining10, 480, 358);
        Lining lining11 = new Lining();
        addObject(lining11, 596, 359);
        Lining lining12 = new Lining();
        addObject(lining12, 740, 354);

        Border border = new Border();
        addObject(border, 0, 180);
        Border border2 = new Border();
        addObject(border2, 770, 180);
    }
}

Thats a copy of the main class, and here is the subclass the counters are used in?

    import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)


public class WhiteCell extends Actor
{
    /**
     * Act: move up and down when cursor keys are pressed.
     */
    public void act() 
    {
        checkKeyPress();
        checkCollision();
    }

    /**
     * Check whether a keyboard key has been pressed and react if it has.
     */
    private void checkKeyPress()
    {
        if (Greenfoot.isKeyDown("up")) 
        {
            setLocation(getX(), getY()-8);
        }

        if (Greenfoot.isKeyDown("down")) 
        {
            setLocation(getX(), getY()+8);
        }

        if (Greenfoot.isKeyDown("right")) 
        {
            setLocation(getX()+4, getY());
        }

        if (Greenfoot.isKeyDown("left")) 
        {
            setLocation(getX()-4, getY());
        }
    }

    /**
     * Check whether we are touching a bacterium or virus. Remove bacteria.
     * Game over if we hit a virus.
     */
    private void checkCollision()
    {
        if (isTouching(Bacteria.class)) 
        {
            Greenfoot.playSound("slurp.wav");
            removeTouching(Bacteria.class);
            Bloodstream bloodstream = (Bloodstream)getWorld();
            bloodstream.addScore(1);
            bloodstream.setNumberOfBacteriaTouched(+1);
        }

        if (isTouching(Virus.class)) 
        {
            removeTouching(Virus.class);
            Bloodstream bloodstream = (Bloodstream)getWorld();
            bloodstream.addScore(-2);
            bloodstream.setNumberOfVirusTouched(+1);
        }
    }
}

Thanks for the help!

Answer 1

If you look at the setter code, it is meant to set the value and not increment it. It is setting the value of numberOfBacteriaTouched to 1 every time it is executed. This is why your counter works for the first time, but does not count pass one.

    public void setNumberOfBacteriaTouched(int numberOfBacteriaTouched)
    {
        this.numberOfBacteriaTouched = numberOfBacteriaTouched;
    }

The correct way to increment the value will be to get the value using the getter, add one to the value and set it using the setter.

    bloodstream.setNumberOfBacteriaTouched(bloodstream.getNumberOfBacteriaTouched()+1);
    bloodstream.setNumberOfVirusTouched(bloodstream.getNumberOfVirusTouched()+1);

Alternatively, you can also write a different method that increments the variable by 1.

    public void incrementNumberOfBacteriaTouched()
    {
        this.numberOfBacteriaTouched++;
    }

Answer 2

public void setNumberOfBacteriaTouched(int numberOfBacteriaTouched)
{
    this.numberOfBacteriaTouched = numberOfBacteriaTouched;
}

Take a look at what that method is doing. It's setting the number touched to whatever value you passed in. You're not adding the value, you're setting a completely new one.

Answer 3

You are reinitializing the class Bloodstream every time you checkCollision() is called. Try to move the instantiation out of checkCollision() method

    private Bloodstream bloodstream;
      onCreate(){
      bloodstream = (Bloodstream)getWorld();          
   } 
   private void checkCollision(){
        if (isTouching(Bacteria.class)) 
        {
            Greenfoot.playSound("slurp.wav");
            removeTouching(Bacteria.class);
            bloodstream.addScore(1);
            bloodstream.setNumberOfBacteriaTouched(+1);
        }

        if (isTouching(Virus.class)) 
        {
            removeTouching(Virus.class);
            bloodstream.addScore(-2);
            bloodstream.setNumberOfVirusTouched(+1);
        }
    }