Queue implementation, enqueue method not working

Question

I am trying to write my own queue class. My enqueue method is only enqueue-ing one object and then if I try to enqueue anything else, its almost as if its ignoring it. Here is my code:

public class myQueue {

    private Node front;
    private Node back;
    private int s;

    public myQueue() {
            front = null;
            back = null;
            s = 0;
    }

    public void enqueue(Object x) {
        if( isEmpty() )
            back = front = new Node(x);
        else
            back = back.next = new Node(x);
        s++;
    }

    public Object dequeue() {
        Object x;
        if( isEmpty() ) { System.out.println("nothing to dequeue.\nqueue empty."); }
        x = front.data;
        s--;
        return x;
    }

    public boolean isEmpty() {
        if(s == 0)
            return true;
        else
            return false;
    }

    public void printQueue() {
        if ( isEmpty() )
            System.out.println("empty queue");
        else {
            Node temp = back;
            while(temp != null) {
                System.out.println(temp);
                temp = temp.next;
            }
        }   
    }



}

and here is my main method where i try to enqueue some objects:

public static void main(String[] args) {
    int a = 5;
    String b = "yo";
    Object c = 5.5;                
    int d = 2;
    String e = "Pen";
    Object f = 9.2;

    myQueue q = new myQueue();

    q.enqueue(a);
    q.enqueue(b);
    q.enqueue(c);
    q.enqueue(d);
    q.enqueue(e);
    q.enqueue(f);

    System.out.println("\n");

    q.printQueue();
}

and then all i get for output is:

data: 9.2

any ideas as to why this is happening?

Cyrille Ka · Accepted Answer · 2013-02-22 01:54:38Z

2

When you print, you are starting at the back of the queue, you should start at the front:

        Node temp = front; // <<< replacing back by front
        while(temp != null) {
            System.out.println(temp);
            temp = temp.next;
        }

If you start at the back of the queue, you will only have the last element of the queue to be printed...

My result with the fix:

data : 5
data : yo
data : 5.5
data : 2
data : Pen
data : 9.2

edited Feb 22, 2013 at 1:54

answered Feb 22, 2013 at 1:49

Cyrille Ka

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1 Comment

Ted Over a year ago

ah that seems so obvious, thanks. For whatever reason i had them drawn in my notebook linked back to front, not front to back, so i was thinking i had to print starting from the back. thank you!

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