在定义变量之前访问变量的问题

Question

我有这个:

public class Sprite

{
    protected float x;
    protected float y;
    protected Image image;
    protected Rectangle boundingBox;


    public Rectangle getBoundingBox()
    {
         boundingBox = new Rectangle(x, y,
                    image.getWidth(), image.getHeight());
        return boundingBox;
    }

但是,当我运行它时,我得到一个空指针异常.类精灵从不单独使用,仅用作超类.

定义图像的唯一方法是通过构造函数:

Sprite(float x, float y, Image image) {
    this.x = x;
    this.y = y;
    this.image = image;
}

Answer 1

可能是因为变量image从未初始化.因此image.getWidth(),image.getHeight()将失败与NullPointerExceptions.初始化变量.或在您尝试使用之前传入image或检查null.