DynamicList/LinkedList Queue Implementation

Question

here is my LinkedList Queue Implementation , seems like its almost like the linkedlist implementation with little differences mainly in the poll() method, i think that the offer() method is same like the linkedlist method add() , the point is that in the offer() method we are adding the elements to the tail, than we are moving them to the left, but their next is same like the add() method, where we are adding in the head and moving the elements to the right... Is i'm right? I'm glad to hear any suggestations...

import java.util.NoSuchElementException;

public class DynamicQueue {

private class Node {
    private Object item;
    private Node next;

    Node(Object item){
        this.item = item;
        this.next = null;
    }

    Node(Object item, Node prevNode){
        this.item = item;
        prevNode.next = this;
    }
}

private Node head;
private Node tail;
private int count;

public DynamicQueue() {
    this.head = null;
    this.tail = null;
    this.count = 0;
}

public int size() {
    return count;
}

public void offer(Object item) {
    if(tail == null) {
        tail = new Node(item);
        head = tail;
    }else {
        Node newNode = new Node(item,tail);
        tail = newNode;
    }
    count++;
}

public void clear() {
    head = null;
}

public Object peek() {
    if(head == null) {
        throw new NoSuchElementException("Overflow Exception");
    }else {
        return head.item;
    }
}

public void poll() {
    if(head == null) {
        throw new NoSuchElementException("Overflow Exception");
    }
    Node currentNode = head.next;
    head.next = null;
    head = currentNode;
    count--;

}

public static void main(String[] args) {
    DynamicQueue queue = new DynamicQueue();
    queue.offer("First");
    queue.offer("Second");
    queue.offer("Third");
    queue.offer("Fourth");
    queue.poll();
    System.out.println(queue.peek());
    queue.poll();
    System.out.println(queue.peek());
    queue.poll();
    System.out.println(queue.peek());

}

}

Answer 1

clear() is buggy

The following code causes a NoSuchElementException:

DynamicQueue queue = new DynamicQueue();
queue.offer("First");
queue.clear();
queue.offer("First");
queue.poll();

You can ealy fix it by adding tail = null; to your clear() method.

Use selfexplaing exception messages

An exception name (in this case NoSuchElementException) already describes the kind of error accurred. The cause should explain why this happened. A better message for exaple could simply be "this queue is empty".

Suggestion: add a return type to poll()

If poll() returns the current head, the user doesn't need to do call peek(). This wouldn't even change your main(String[]), since the user is not forced to use the returned object at all.

---

Of course, you could also add a generic type to your class instead of using Object inside your Node, but I guess that was not your intension, since you are already familiar with the Java Collections.