在遍历双向链表时如何跳过空虚拟节点

Question

I have a doubly linked list which looks like:

null 1 2 3 null

When I traverse the list using an iterator with the code below, the output prints exactly what is written above.

            Iterator<Integer> it = lst.iterator(); // tests iterator method
            while (it.hasNext()) {
              Integer val = it.next();

              System.out.println(val);
            }

However, I want to skip the null nodes as I traverse the list so that it only prints:

1 2 3

I cannot get my code to do that. Here is what I have come up with so far.

            Iterator<Integer> it = lst.iterator(); // tests iterator method
            while (it.hasNext()) {
              Integer val = it.next();
              if (val == null)
                 it.next()

              System.out.println(val);
            }

The problem with that is that I get a NoSuchElementException error, but I cannot figure out how to fix it. My guess is I get that error because when I get to the second null dummy node, I try to skip it, but there are no other nodes to jump to.

My question is, how can I change my code so that it prints each element in the doubly linked list while skipping both of the null dummy nodes?

Answer 1

All you have to do is to use the test in combination with the println:

while (it.hasNext()) {
   Integer val = it.next();
   if (val != null){
       System.out.println(val);
   }
}

If you do an extra next in the loop, you skip one hasNext, and that's why you run into the exception.