Java ArrayIndexOutOfBounds 错误

Question

所以我有一个数组 Canvas[256][256]，它的随机索引 Canvas[r][r] (r 是随机的)设置为 1。然后我想循环遍历该数组以准确查看哪个索引是不是 0，然后随机选择一个点(上、下、左、右)并将该点也设置为 1。它在第一个循环中工作得很好，但之后给了我一个数组越界错误。

public static void checkPopulation() {
    for(int x = 0; x < Canvas.length; x++) {
        for(int y = 0; y < Canvas.length; y++) {
            if(Canvas[x][y] != 0) {
                particleDiffusion(x, y);
            }
        }
    }

}

public static void particleDiffusion(int x, int y) {
    Random r = new Random();
    if(r.nextInt(3) == 0) {
        Canvas[x+1][y] = 255;
    } else if(r.nextInt(3) == 1) {
        Canvas[x][y+1] = 255;
    } else if(r.nextInt(3) == 2) {
        Canvas[x-1][y] = 255;//THIS IS WHERE ERROR IS POINTING
    } else if(r.nextInt(3) == 3) {
        Canvas[x][y-1] = 255;
    }
    if(stepsTaken < diffusionStep) {
        checkPopulation();
    } else {
        System.out.println("done");
        return;
    }
}

有人可以帮我解决我做错的事情吗？为什么它循环一次然后给出错误？

Answer 1

你检查x和y是否小于Canvas.length，然后你使用x+1和y+1作为数组索引，这就是原因。固定代码如下。

public static void checkPopulation() {
    for(int x = 0; x < Canvas.length; x++) {
        for(int y = 0; y < Canvas.length; y++) {
            if(Canvas[x][y] != 0) {
                particleDiffusion(x, y);
            }
        }
    }
}

public static void particleDiffusion(int x, int y) {
    Random r = new Random();
    if(r.nextInt(3) == 0) {
        if( x+1 < Canvas.length)
            Canvas[x+1][y] = 255;
    } else if(r.nextInt(3) == 1) {
        if( y+1 < Canvas.length)
            Canvas[x][y+1] = 255;
    } else if(r.nextInt(3) == 2) {
        if( x > 0)
            Canvas[x-1][y] = 255;//THIS IS WHERE ERROR IS POINTING
    } else if(r.nextInt(3) == 3) {
        if( y > 0)
            Canvas[x][y-1] = 255;
    }
    if(stepsTaken < diffusionStep) {
        checkPopulation();
    } else {
        System.out.println("done");
        return;
    }
}

编辑:您还应该检查 x-1 和 y-1 不是负数。