normal queue

class HMQueue {
    private static QueueNode tail = null, head = null;

    public static int dequeue() {
        if (head == null) {
            return -1;
        }
        QueueNode temp = head;
        head = head.next;
        if (head == null) {
            tail = null;
        }
        return temp.data;
    }

    public static void enqueue(int item) {
        QueueNode node = new QueueNode(item);
        if (head == null) {
            head = node;
        }
        else {
            tail.next = node;
        }
        tail = node;
    }

    public static int peek() {
        if (head == null) {
            return -1;
        }
        return head.data;
    }

    public static boolean isEmpty() {
        return tail == null && head == null;
    }

}

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class QueueNode {
    int data;
    QueueNode next;
    public QueueNode(int data) {
        this.data = data;
        this.next = null;
    }
}