Question

这是我隔离的代码：

public static void randomIntArray(int n) {
    int[] a = new int[n];
    for (int i = 0; i < a.length; i++) {
        a[i] = randomInt(-5, 15);
    }
    scoreHist(a);
}

public static void scoreHist(int[] scores) {
    int[] counts = new int[30];
    for (int i = 0; i < scores.length; i++) {
        int index = scores[i];
        counts[index]++;
    }
}

但每当我运行它时，它就会给我这个：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: (Insert Random # Here)
    at arrayhistogram.ArrayHistogram.scoreHist(ArrayHistogram.java:39)
    at arrayhistogram.ArrayHistogram.randomIntArray(ArrayHistogram.java:31)
    at arrayhistogram.ArrayHistogram.main(ArrayHistogram.java:21)

我迷失了。想法？我真的被困住了，现在已经和他们一起玩了一段时间。

Answer 1

int index = scores[i];
counts[index]++;

根据randomInt（-5,15），索引可能是负数。

Answer 2

更改

counts[index]

到

counts[index + 5]

这是因为index来自a数组，其元素初始化为-5和14之间的值。但是，只允许0和29之间的值作为counts的索引，因此您需要添加5。

Answer 3

所以这就是你的代码所做的事情：

你从-5到15中选择'n'个随机数（比如n = 5），将它们推入数组

说，阵列变为

scores[] = {0,1,1,5,-3}

现在，您将在scoreHist()。

中传递此创建的数组

现在，查看运行期间的变量状态

   i       scores[i]        index               counts[index]
  ---      ---------        -----           ----------------------
//1st iteration
   0      scores[0]=0         0           counts[0]=counts[0]+1 -> 1       
Everything goes fine in the first iteration.
//2nd iteration
   1      scores[1]=1         1           counts[1]=counts[1]+1 -> 1
Everything goes fine here as well. Now "counts[] = {1,1}"
//3rd iteration
   2      scores[2]=1         1           counts[1]=counts[1]+1 -> 2
Things go alright. counts[1] has been updated. Now "counts[] = {1,2}"
//4th iteration
   3      scores[3]=5         5           counts[5]=counts[5]+1 -> 1
Things go absolutely fine here . 
//5th iteration
   4      scores[4]=-3        -3          counts[-3] !!!!!!!! It is out of bound limits for the       
                                                              array. This index does not exist.

这就是导致你有异常的原因希望这会有所帮助。

直方图项目：代码抛出ArrayIndexOutOfBoundsException

3 个答案: