ThreadSafeQueue.java

package com.thealgorithms.datastructures.queues;

public class ThreadSafeQueue<T> {

    private static class Node<T> {
        T data;
        Node<T> next;

        Node(T data) {
            this.data = data;
        }
    }

    private Node<T> head;
    private Node<T> tail;

    public synchronized void enqueue(T data) {
        Node<T> newNode = new Node<>(data);

        if (tail == null) {
            head = newNode;
            tail = newNode;
            return;
        }

        tail.next = newNode;
        tail = newNode;
    }

    public synchronized T dequeue() {
        if (head == null) {
            return null;
        }

        T data = head.data;
        head = head.next;

        if (head == null) {
            tail = null;
        }

        return data;
    }

    public synchronized boolean isEmpty() {
        return head == null;
    }
}