将迭代器转换为Integer-ConcurrentModificationException

Question

I am trying to find the second biggest element in a list using recursion and an Iteration:

static List<Integer> list = new ArrayList<Integer>();
static Iterator<Integer> it = list.iterator();

public static int secondBiggest(List<Integer> a) {
    if(it.hasNext()) {
        Integer cur = it.next();

        if (cur > biggest) {
            secondBiggest = biggest;
            biggest = cur;
        } else if (cur < biggest && cur > secondBiggest) {
            secondBiggest = cur;
        }
        secondBiggest(a);
    }
    return secondBiggest;
}

What I get is a

ConcurrentModificationException at java.base/java.util.ArrayList$Itr.checkForComodification(Unknown Source) at java.base/java.util.ArrayList$Itr.next(Unknown Source)

in line 6 in the code previously mentioned

Answer 1

The exit for recursion is not right, it can't get to the end: if(it.hasNext())

If you really want to implement by recursion, You can use the following example:

public void test() {
    List<Integer> integers = Arrays.asList(1, 4, 1234, 5, 6, 77);
    int secondBiggest = second(integers, -1, 0, 0);
    System.out.println(secondBiggest);
}


public Integer second(List<Integer> a, Integer biggest, Integer secondBiggest, Integer length) {
    if (a.size() > length) {
        Integer cur = a.get(length);
        length++;
        if (cur > biggest) {
            secondBiggest = biggest;
            biggest = cur;
        } else if (cur < biggest && cur > secondBiggest) {
            secondBiggest = cur;
        }
        secondBiggest = second(a, biggest, secondBiggest, length);
    }
    return secondBiggest;
}