Question

所以我有一个处理按钮的类，我有一个包含2个单独矩形的矩形数组。现在，当我创建一个检索数据的第0个索引的变量时，它会给我一个nullpointerexception，我一直在摸着头，我已经清楚地声明并初始化了数组并使其成为2个矩形的适当大小。已将这些分配给索引。我必须遗漏一些我似乎无法弄清楚的小东西。

下面我已经为此提供了相关代码：

public class MenuButton {

private int height;
private int width;
private float positionX;
private float positionY;

//private ArrayList<Rectangle> rects;
private Rectangle rects[];

private Rectangle play;
private Rectangle touchToPlay;

private boolean isTouched;

public MenuButton(int height, int width, float positionX, float positionY){

    this.height = height;
    this.width = width;
    this.positionX = positionX;
    this.positionY = positionY;

    isTouched = false;
    Rectangle rects[] = new Rectangle[2];
    play = new Rectangle(positionX, positionY, width, height);
    touchToPlay = new Rectangle(positionX, positionY, width, height);


    //can clean this up by introducing initButtons() to assign buttons to
    //indexes of the array
    rects[0] = play;
    rects[1] = touchToPlay;

}   


public boolean isClicked(int index,float screenX, float screenY){

    //ERROR IS BELOW THIS LINE  
    Rectangle rect = rects[0];

    return rect.contains(screenX, screenY);
}

Answer 1

你shadowing变量rects。取代

Rectangle rects[] = new Rectangle[2];

与

rects = new Rectangle[2];

Answer 2

是的，rects变量是MenuButton构造函数的本地变量（我假设它是构造函数）。这意味着它隐藏了您在类中声明的具有相同名称的字段。所以你初始化了局部变量，然后在构造函数的末尾，它就消失了。该领域仍然是空的。

Answer 3

您已宣布Rectangle rects[]两次。只需将构造函数中的行更改为rects = new Rectangle[2];

即可

nullpointerexception从矩形数组中检索矩形时

3 个答案: