Stack

A stack is a linear data structure that follows the LIFO (Last In, First Out) principle: the element added last is the first one removed. Elements are added with a push operation and removed with a pop operation, both at the same end, called the top.

Stacks are used for function calls (the call stack), undo features, expression evaluation, matching brackets and backtracking algorithms.

import java.util.ArrayDeque;
import java.util.Deque;

Deque<Integer> stack = new ArrayDeque<>();
stack.push(1);
stack.push(2);
stack.push(3);
System.out.println(stack.pop());  // 3 (last in, first out)
System.out.println(stack.peek()); // 2