In java, can nested class object use the enclosing class method?

I created a simple list class. What I want to do is to create a method in SLList to give the size a SLList object. I want to do it recursively, however, the following size() method I created just does not work. I know other ways to realize it such as creating a helper method. But what I am curious about is that why does my size() does not work? The error message is the "size() is undefined for SLList.IntNode". Why? Since I made the nested IntMode class just public and non-static, why it cannot use the method that is defined in SLList class?

public class SLList {

    public class IntNode {

        public int item;
        public IntNode next;

        public IntNode(int i, IntNode n) {
            item = i;
            next = n;
        }
    }

    private IntNode first;

    public SLList(int x) {
        first = new IntNode(x, null);
    }

    public int size() {
        if (first.next == null) {
           return 1;
        }
        return 1 + first.next.size();
    }
}

I am just new to Java, and quite confused about the private and static things, especially when it comes to the Class. Thank you for anyone answering me.

You can fiddle it by adding an extra private method but it's not particularly easy to reason about. I would avoid doing it this way unless absolutely necessary.

class SLList {

    public class IntNode {

        public int item;
        public IntNode next;

        public IntNode(int i, IntNode n) {
            item = i;
            next = n;
        }

        private int theSize()
        {
            return size();
        }
    }

    private IntNode first;

    public SLList(int x) {
        first = new IntNode(x, null);
    }

    public int size() {
        if (first.next == null) {
            return 1;
        }
        return 1 + first.next.theSize();
    }
}