Unit tests and DequeBasedSynchronizedStack added up

core-java-collections/src/main/java/com/baeldung/thread_safe_lifo/DequeBasedSynchronizedStack.java

@@ -0,0 +1,36 @@
+package com.baeldung.thread_safe_lifo;
+
+import java.util.ArrayDeque;
+
+/**
+ * Deque Based Stack implementation.
+ */
+public class DequeBasedSynchronizedStack<T> {
+
+    // Internal Deque which gets decorated for synchronization.
+    private ArrayDeque<T> dequeStore = new ArrayDeque<>();
+
+    public DequeBasedSynchronizedStack(int initialCapacity) {
+        this.dequeStore = new ArrayDeque<>(initialCapacity);
+    }
+
+    public DequeBasedSynchronizedStack() {
+
+    }
+
+    public synchronized T pop() {
+        return this.dequeStore.pop();
+    }
+
+    public synchronized void push(T element) {
+        this.dequeStore.push(element);
+    }
+
+    public synchronized T peek() {
+        return this.dequeStore.peek();
+    }
+
+    public synchronized int size() {
+        return this.dequeStore.size();
+    }
+}