Stack

Java provides an inbuilt object type called Stack. It is a collection that is based on the last in first out (LIFO) principle. On Creation, a stack is empty.

Operations

Function	What it does?	Complexity
Object push(Object element)	Pushes an element on the top of the stack.	O(1)
Object pop()	Removes and returns the top element of the stack. An ‘EmptyStackException’ exception is thrown if we call pop() when the invoking stack is empty.	O(1)
Object peek( )	Returns the element on the top of the stack, but does not remove it.	O(1)
boolean empty()	It returns true if nothing is on the top of the stack. Else, returns false.	O(1)
int search(Object element)	It determines whether an object exists in the stack. If the element is found, it returns the position of the element from the top of the stack. Else, it returns -1.	-

Implementions

import java.io.*;
import java.util.*;
 
class Main
{   
    public static void main (String[] args)
    {
        Stack<Integer> stack = new Stack<Integer>();
 
        stack.push(10);
        stack.push(3);
        stack.push(5);
        stack.push(20);
        System.out.println("Current Stack [  bottom to top ]");
        for(Integer i : stack){
            System.out.print(" "+i);
        }
        System.out.println("Popped : "+ stack.pop());
        stack.push(7);
        System.out.println("Peak : " + stack.peek()) ;
        System.out.println("Element 3 at position : " + stack.search(3));
    }
}

Output:

Current Stack
10 3 5 20
Popped : 20
Peak : 7
Element 3 at position : 3