Iterating through LinkedList in Java

Question

Let me first apologize if this is ridiculously elementary. This is my first time programming.

The issue here is that I need to print out a LinkedList. Could someone guide me as to what I'm doing wrong? Here's what I have:

public class Queue {
private LinkedList list;
public Queue() { 
 list = new LinkedList(); 
}
}
public class BankQueue {
static Queue q = new Queue();
public static void main(String[] args) {
 //Insert a menu with a list of possible choices
public static void printQueue(Queue q) {
 for (String s : q) {
 System.out.println(q);
 }
}

I keep getting errors saying that say that I can only iterate over an array or an instance of java.lang.Iterable. Thanks for the help. It's sincerely appreciated.

Answer 1

You need to iterate over a list, not over your class instance that in fact doesn't implement Iterable, like

public void printQueue(Queue q) {
 for(String s : q.getList()) {
 //do anything with your string
 }
}

Of course, it implies that your LinkedList is in fact LinkedList<String> and that you have a getter for list field declared in your class like public List<String> getList() { return list; }.

• TheExecutive2011: I had to add the getter, but that fixed my issue. Thanks for the help!

Answer 2

Your class Queue is not iterable.

Incidentally, its name collides with java.util.Queue, which is iterable.

If you're actually trying to iterate over the list member of Queue, you'll need to provide a getter for that (it's private), or write yourself a Visitor.

• TheExecutive2011: I actually did not realize that there was already a use for "Queue". Perhaps I'll change the name of this thing...

Answer 3

You don't appear to be iterating over the list member of q. You would need to implement the Iterable interface, or iterate over q.list directly.

The really proper way to do it would be to implement Iterable.

Answer 4

You need to use iterator to loop through the LinkedList like below:

iterator = q.iterator(); 
 while (iterator.hasNext()) {
 System.out.print(iterator.next()+" "); 
}

• GriffeyDog: The OP has defined his own Queue class, which doesn't implement Iterable, and therefore does not have an iterator() method.
• TheExecutive2011: Ah. That explains why I couldn't get that to work. Sorry for the confusion with the class name. I didn't realize that there was already a use for "Queue". Thanks anyway.