feat: add simple thread-safe queue using synchronized

Author: prashantpiyush1111

src/main/java/com/thealgorithms/datastructures/queues/ThreadSafeQueue.java

@@ -0,0 +1,47 @@
+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 = 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;
+    }
+}

src/test/java/com/thealgorithms/datastructures/queues/ThreadSafeQueueTest.java

@@ -0,0 +1,26 @@
+package com.thealgorithms.datastructures.queues;
+
+public class ThreadSafeQueueTest {
+
+    public static void main(String[] args) {
+
+        ThreadSafeQueue<Integer> queue = new ThreadSafeQueue<>();
+
+        Thread producer = new Thread(() -> {
+            for (int i = 1; i <= 5; i++) {
+                queue.enqueue(i);
+                System.out.println("Enqueued: " + i);
+            }
+        });
+
+        Thread consumer = new Thread(() -> {
+            for (int i = 1; i <= 5; i++) {
+                Integer val = queue.dequeue();
+                System.out.println("Dequeued: " + val);
+            }
+        });
+
+        producer.start();
+        consumer.start();
+    }
+}