Question

我正在尝试制作2D平铺游戏，在制作包含贴图的数组时，我得到一个NullPointerException，这里有一些代码。对不起，如果格式不正确，请先使用计时器

公共课世界{

//holds data for where to place images and rectangles
int[][] worldDat = new int[25][25]; 
//hold rectangles for checking interaction with player
Rectangle[][] blocks = new Rectangle[25][25];
//holds block's images to be painted
Image[][] blockImage = new Image[25][25];
//holds position to be pained on screen
int[][] location = new int[25][25];
//enumeration holding block's images and other things of the sort
EWorldBlocks eBlocks;

//sets all of the arrays listed above
public void setupAll(){

    for(int i = 0; i < 24; i++){

        for(int e = 0; e < 24; e++){                    
            blocks[i][e].setBounds(e * 20, i * 20, 20, 20);
            blocks[i][e].setLocation(e*20, i*20);

            if(worldDat[i][e] == 6){
                blockImage[i][e] = getRandomGrass();
            }else if(worldDat[i][e] == 0){
                blockImage[i][e] = null;
            }else{
            blockImage[i][e] = eBlocks.intToImage(worldDat[i][e]);
            }
        }
    }
}   

//used to get a random block
private Image getRandomGrass()
{
    Random rand = new Random();

    int r = rand.nextInt(2);
    r++;

    return eBlocks.intToImage(r);
}


public World(int[][] worldDat) {
    this.worldDat = worldDat;
}

}

然后在这个类中调用（我相信它的一部分问题）

public class worldDraw {

//ALSO if there is a better way to do this, do tell
levels levels = new levels();
static levels sLevels = new levels();
World level1;
static World sLevel1 = new World(sLevels.getLevel1());

//called in paint method for panel
public void draw(Graphics2D g2){
    sLevel1.setupAll();
    for(int i = 0; i < 24; i++){
        for(int e = 0; i < 24; i++){
            g2.drawImage(level1.blockImage[i][e], e*25, i*25, null);
        }
    }

}

//holds levels
public worldDraw() {        
    level1 = new World(levels.getLevel1());
}
}

Answer 1

创建对象数组时，您正在创建引用数组，但您没有分配引用。在尝试使用它们之前，您必须先执行此操作。可以认为它类似于创建一个鸡蛋盒。在您首先用鸡蛋填充纸箱之前，您不能使用任何鸡蛋。因此，例如你的块数组，首先需要将Rectangle对象分配给数组中的每个项目，然后才能调用它们上的方法。这通常在for循环中完成。例如，

for(int i = 0; i < 24; i++){
    for(int e = 0; e < 24; e++){       
        blocks[i][e] = new Rectangle(....); //...             
        blocks[i][e].setBounds(e * 20, i * 20, 20, 20);
        blocks[i][e].setLocation(e*20, i*20);

Answer 2

你需要知道Java不像C。

执行此操作时：

Rectangle[][] blocks = new Rectangle[25][25];

块2D数组中的所有引用都为null，直到您调用new并为它们提供引用。

所以你必须这样做：

for(int i = 0; i < 24; i++){
    for(int e = 0; e < 24; e++){             
        blocks[i][e] = new Rectangle(); // I don't know what arguments it takes.       
        blocks[i][e].setBounds(e * 20, i * 20, 20, 20);
        blocks[i][e].setLocation(e*20, i*20);

初始化2D对象数组时出现空指针异常[Java]

2 个答案: