Hello, dear student! Today's lesson will take you on an exciting journey through Stacks, a powerful tool in Java. In programming, Stacks are fundamental data structures utilized in various applications. Our goal for this lesson is to understand the concept of Stacks, learn how to implement and manipulate them in Java and delve deep into their complexities. Let's get started!

First and foremost, let's understand what a Stack is. Imagine a stack of plates that you can only remove from the top. That's precisely what a Stack is: a Last-In, First-Out (LIFO) structure. Stacks are used in memory management, backtracking algorithms, and more. The key operations involved are Push (adding an element to the top of the stack), Pop (removing the topmost element), and Peek (looking at the topmost element without removing it).

Java provides two common ways to implement Stacks: Array-based and Linked-list-based. In the former, we use an array to store the elements to create the Stack; in the latter, we use a linked list instead. Let's look into creating a Stack using an array in Java:

top represents the index in the stackArray that is currently the top element of the stack. It is initialized to -1, showing the stack is empty, and there is no valid index for the top element.