Java:为什么这个列表落后于我的游戏 “Out of Memory”

Question

你好，我正在尝试在玩家后面添加一条尾部，就像贪吃蛇游戏一样。但由于某种原因，这使我的游戏持续滞后并耗尽内存。为什么会发生这种情况以及如何解决这个问题？

我像这样创建列表:

List<Snake> snake = new CopyOnWriteArrayList<Snake>();

这是我创建新对象并在 forloop 中删除它们的地方:

public void snake() {
    snake.add(new Snake(ball.getX(), ball.getY()));
    currentTime++;
    for(Snake currentSnake: snake) {
        if(currentSnake.creationDate < SnakeLength){
            currentSnake.Update();
        } else {
            Gdx.app.log("SnakeLength" + SnakeLength, "CreationDate" + currentSnake.creationDate);
            snake.remove(currentSnake);
        }
    }
}

这就是我的蛇类的样子:

public class Snake
{
    float width = Gdx.graphics.getWidth();
    float height = Gdx.graphics.getHeight();
    float screenwidth = width/270;
    float screenheight = height/480;

    public float x;
    public float y;
    public int creationDate;
    ShapeRenderer shapeRenderer;
    SpriteBatch batch;

    public boolean active = false;

    public Snake(float x, float y) {
        shapeRenderer = new ShapeRenderer();
        batch = new SpriteBatch();
        this.x = x;
        this.y = y;
    }

    public void Update() {
        batch.begin();
        shapeRenderer.begin(ShapeType.Filled);
        shapeRenderer.setColor(new Color(1, 1, 1, 0.2f));
        shapeRenderer.circle(x + 8*screenwidth, y + 8*screenheight, 6*screenheight);
        shapeRenderer.end();
        batch.end();
        creationDate++;
    }
}

Answer 1

如javadoc所述CopyOnWriteArrayList :

A thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array.

因此，这是一个成本高昂的操作，并且该类专为并发读取而设计，修改率较小。看起来这不是你的情况。

如果您选择此类来解决在修改列表时读取列表的问题，请考虑将迭代器与专为该用途而设计的 ArrayList 一起使用:

synchronized(snake) { // Protect the snake list against concurrent access. Do it whenever you access the snake list
  for(Iterator<Snake> it = snake.iterator();; it.hasNext()) {
    Snake currentSnake = it.next();
    if(currentSnake.creationDate < SnakeLength) {
        currentSnake.Update();
    } else {
        Gdx.app.log("SnakeLength" + SnakeLength, "CreationDate" + currentSnake.creationDate);
        it.remove();
    }
  }
}

请注意，ArrayList 没有针对并发访问的保护。如果多个线程能够读取和写入您的列表，您必须使用同步块(synchronized block)来保护它。

但是阅读你的代码，我想带有 PriorityQueue 的设计似乎更合适。