CODEWITHSUNDEEP
javaforeachiteratoriterable
J_Tarasovic
J_Tarasovic

Reputation: 114

Java Iterator Not Working With Single Iterable Object

I am having a problem with Iterators. I am writing a custom linked list as using an iterator to be able to traverse the list.

The iterator looks like this:

public class NodeIterator implements Iterator<Node> {
private Node current = head;
private Node lastReturned = head;

public boolean hasNext() {
    return lastReturned.getLink() != null;
}

public Node next() {
    lastReturned = current;
    current = current.getLink();
    return lastReturned;
}

public void remove() {
    removeNode(lastReturned);
    lastReturned = null;
}
}

I'm still in the early stages so I'm testing the data structures from the console by populating the nodes with this method.

private static void MethodToPopulateNodes() {
MyObject o = new MyObject();
String[] responses = new String[prompts.length];
scanner = new Scanner(System.in);

boolean done = false;
String s = null;

while (!done) {
    int i = 0;
    for (String prompt : prompts) {
        System.out.println(prompt);
        s = scanner.nextLine();
        if (s.equalsIgnoreCase("stop")) {
            done = true;
            break;
    } else {
        responses[i] = s;
    }
        i++;
    }
    if (done) {
        break;
    }
        o = new MyObject(responses);
        myNode.add(c);
}
}

When I try to use the iterator when there is only one Node, it doesn't do anything. No errors or anything. However, if I have multiple nodes, this foreach works flawlessly.

public static void main(String[] args) {
myNode = new Node();

methodToPopulateLinkedList();

for (Node node : myNode) {
        //toString is overridden for my object
    System.out.println(node.getData().toString());
}

}

UPDATE: I edited the iterator to return hasNext() == true on the first iteration:

public class NodeIterator implements Iterator<Node> {
private boolean done = false;
private Node current = head;
private Node lastReturned = head;

public boolean hasNext() {
    if (head == tail && head != null && !done) {
    done = true;
    return true;
    }
    return lastReturned.getLink() != null;
}

public Node next() {
    lastReturned = current;
    current = current.getLink();
    return lastReturned;
}

public void remove() {
    removeNode(lastReturned);
    lastReturned = null;
}
}

I feel like that is super janky but it works. It seems like Java calls hasNext() first before calling next so I have to treat the special case differently.

|123

hasNext() == true
next() == 1

1|23

hasNext() == true
next() == 2

12|3

Where | equals the cursor. Is that accurate? Is there a better way to solve this?

Upvotes: 0

Views: 1056

Answers (1)

roguequery
roguequery

Reputation: 974

If there's just one Node, it would have the special case of its ->next being null. Before the loop, try printing out the first node, I think your loop might be looking one ahead.

Upvotes: 2

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