ReverseStack.java

import java.util.Stack;

public class ReverseStack {

    public static void reverseStack(Stack <Integer> s){
        Stack <Integer> st = new Stack<>();
        while(!s.isEmpty()){
            st.push(s.pop());
        }

        while(!st.isEmpty()){
            System.out.println(st.peek());
            st.pop();
        }
    }

    public static void pushBottom(Stack <Integer> s, int data){
        if(s.isEmpty()){
            s.push(data);
            return;
        }
        int top = s.pop();
        pushBottom(s, data);
        s.push(top);
    }
    public static void reverseStackoptimised(Stack <Integer> s){
        if(s.isEmpty()){
            return;
        }

        int top = s.pop();
        reverseStackoptimised(s);
        pushBottom(s, top);
    }
    public static void main(String args[]){
        Stack <Integer> s = new Stack<>();
        s.push(1);
        s.push(2);
        s.push(3);
        s.push(4);
        reverseStackoptimised(s);
        
        while(!s.isEmpty()){
            System.out.println(s.peek());
            s.pop();
        }

    }
}