Java射击游戏删除子弹对象

Question

I have a shooting game and when the spacebar is pressed, a bullet object is created. When the bullet object is outside of the screen, I want to delete the object so I can shoot more than 10 times.

Instantiation:

Shot[] shot = new Shot[10];

Spacebar code:

if (key == KeyEvent.VK_SPACE) {
    if (shots < maxShots) {
        if (canShoot) {
            shot[shots] = new Shot(player.x, player.y, player.width, player.height, shotDir);
            shots++;
            canShoot = false;
        }
    }
}

Drawing code:

for (int i = 0; i < shots; i++) {
    if (shot[i].active) {
        shot[i].drawShot(g);
    }
}

Where I want to delete the shot:

for (int i = 0; i < shots; i++) {
    shot[i].shotLoop();
    if (shot[i].outOfBounds(WINDOW_SIZE.width, WINDOW_SIZE.height)) {
        // Delete Bullet
        shot[i].active = false;
    }
}

I tried to do shots--; but when one shot leaves the screen, all shots currently on the screen are deleted. Any suggestions?

Here is the shot[i].outOfBounds() code

public boolean outOfBounds(int screenx, int screeny) {
    if (x < 0 || x > screenx || y < 0 || y > screeny) {
        return true;
    } else {
        return false;
    }
}

Answer 1

Use an ArrayList instead so you can remove it from the list when it goes out of bounds?

ArrayList<Shot> shot = new ArrayList<Shot>();

ArrayList.remove(int index)

You shouldn't remove while iterating over, so you might have to store the index of the objects (or the objects themselves) and remove them after finding the bullets to remove.

Also if you only want 10, you can set a capacity of 10, and just monitor the size to make sure it doesn't go over.

Answer 2

class Weapon
{
    private ArrayList<Shot> magazine;

    private int maxShots;

    private double rotationAngle = 90;
    private double rotationSpeed = 1.5;

    public Weapon(int maxShots)
    {
        this.maxShots = maxShots;

        magazine = new ArrayList<Shot>(maxShots);
    }

    public void rotate(int direction)
    {
        // no need to create hashamp etc to hold "left" or "right"
        // when passing keyPressed, KeyeEvent.getKeyCode is enough.

        // i see alot of people having separate if statements,
        // why, i dont know when you can only go in one
        // direction at a time!

        // also of note, most people wrongly assume that
        // either left or right will be passed, hence, if/else
        // statements.  use "if/else if" to guarantee only 
        // left or right

        if (direction == KeyEvent.VK_LEFT)
        {
            angle-=speed;
        }
        else if (direction == KeyEvent.VK_RIGHT) 
        {
            angle+=speed;
        }
    }

    public void draw(Graphics2D g2, Dimension boundary)
    {
        // do NOT check if shot is out of bounds here,
        // the only thing that should be done in draw,
        // is draw!
    }

    public Iterator<Shot> getMagazine()
    {
        // by returning the iterator, you guarantee
        // concurrency i.e preventing concurrent modifications
        // to data, for example, drawing shots, moving shots
        // and removing them

        return magazine.iterator();
    }

    public void shoot()
    {
        double radian = Math.toRadians(-angle); // invert angle

        double x = [center x] + ([length of weapon] * Math.cos(radian))-[your shot diameter];
        double y = [center y] + ([length of weapon] * Math.sin(radian))-[your shot diameter];

        if (magazine.size() < capacity)
        {
            magazine.add(new Shot(x,y,radian));
        }
    }
}

class Shot extends Ellipse2D.Double
{
    Point2D.Double point;
    Point2D.Double velocity;

    double shotSpeed = 10;

    public Shot(Point2D.Double origin, double radian)
    {
        velocity = new Point2D.Double(Math.cos(radian)*shotSpeed,Math.sin(radian)*shotSpeed);

        point = new Point2D.Double(origin.x+velocity.x,origin.y+velocity.y);

        setFrame(point.x,point.y,[shot diameter],[shot diameter]);
    }

    public void draw(Graphics2D g2)
    {
        g2.setColor(Color.pink);
        g2.fill(this);
    }

    public void move()
    {
        point.x+=velocity.x;
        point.y+=velocity.y;

        setFrame(point.x,point.y,[shot diameter],[shot diameter]);
    }
}


// use javax.swing.Timer to update/paint instead is 
// while(true) with a Thread.sleep.  it allows for stopping and 
// restarting without creating additional objects

public void actionPerformed(ActionEvent event)
{
    // check for rotation......

    // check for shots fired....


    // iterator is faster than conditional loops
    Iterator<Shot> iterator = weapon.getMagazine();

    while(iterator.hasNext())
    {
        Shot shot = iterator.next();

        // getBounds() is the bounds of your panel
        // shot.getBounds() is an inherited method of
        // Ellipse2D.Double

        // use java.awt.geom.RectangleShape.contains(Rectangle) method
        if (getBounds().contains(shot.getBounds()))
        {
            // if the shot is within the rectangle, move it
            shot.move(); 
        }
        else
        {
            iterator.remove();
        }
    }

    // collision detection etc...

    repaint();
}