I don't really understand what this method is doing, can someone please help me explain it? (Arrays + random numbers)

My textbook gave me this code to help count the amount of times a certain number shows up in an array of integers. I tried to apply the code my textbook gave me to my assignment but it doesn't seem to be working. Basically, I have to generate 30 random integers in an array, with the upper bound being 15 and lower bond being -5. I want to find out how many times a number in the array is equal to 0, 1, 2... all the way until 10. The first code is the one my textbook gave me. They also used a random number generator but instead of finding how many elements is equal to 0, 1, etc, they want to find how many times each number appears. (The scores array is simply the random number generator, and their upper bound is 100). The second code is mine.

int[] counts = new int [100];
for (int i = 0; i < scores.length; i++) { 
int index = scores[i]; 
counts[index]++;
}


 //This is my code
 public static void main(String[] args) {
    int []a = arrayHist ();
    printArray (a);
}

public static int randomInt (int low, int high) {
    int range = (high - low) +1;
    return (int) (Math.random() * range) + low;

}

public static int[] randomIntArray (int x) {
    int[] random = new int[x];
    for (int i = 0; i< x; i++) {
        random [i] = randomInt (-5, 15);

    }
    return random;
}

public static int[] arrayHist () {
    int[] counts = new int [30];
    int[] hist = randomIntArray (30);
    for (int i = 0; i < 10 && i >= 0; i++) {
        int index = hist[i];
        counts[index]++;
    }
    return hist;
}


public static void printArray (int[] a) {
    for (int i = 0; i < a.length; i++) {
        System.out.println (a[i]);
    }
}

I'm supposed to be getting only 11 elements, but instead I get 30 random numbers again. Why is that?