• Stack is an ADT (abstract data type) that is a collection of elements where items are added and removed from the end, known as the "top" of the stack.

• Stack works on the principle of LIFO (Last In First Out), it means that the last item added to the stack will be the first item to be removed.

Stack<Obj> stack=new Stack<Obj>();

Stack is based on two functions (methods)-

It adds "element" to the top of the stack.

For example: If we have 1, 3, 5 in stack, and we call push(9),

9 will be added to last index of stack -> 1, 3, 5 , 9.

It returns element at the top of the stack.

For example: If we have 1, 3, 5 in stack, and we call peek(),

5 will be returned (without removing it from the stack).

It removes the last element (i.e. top of stack) from stack.

For example: If we have 1, 3, 5 , 9 in stack, and we call pop(),

the function will return 9 and the stack will change to 1, 3, 5.

• Undo mechanisms: Many software applications use stacks to implement an "undo" feature.

• Browser history: The "back" button in a web browser is implemented using a stack, allowing users to navigate through previously visited pages.

• Function calls and recursion: The computer's call stack keeps track of function calls, allowing programs to remember where to return after a function finishes execution.