package Semester2;

import java.util.Stack;

public class Vorlesung2 {

    private int value;
    private Vorlesung2 nextElement;
    private Vorlesung2 previousElement;

    public Vorlesung2(int value, Vorlesung2 nextElement, Vorlesung2 previousElement) {
        this.value = value;
        this.nextElement = nextElement;
        this.previousElement = previousElement;
    }

    public static void main(String[] args) {
        Vorlesung2 stack = new Vorlesung2(0, null, null);
        stack.push(7);
        stack.push(3);
        stack.push(8);
        stack.push(2);
        System.out.println(stack.pop());
        System.out.println(stack.pop());
        stack.push(7);
        System.out.println(stack.pop());
        System.out.println(stack.pop());
    }


    public void push(int i) {
        if (this.nextElement != null) {
            this.nextElement.push(i);
        } else {
            this.nextElement = new Vorlesung2(i, null, this);
        }
    }


    public int pop() {
        if (this.nextElement != null) {
            return nextElement.pop();
        } else {
            if (this.previousElement != null) {
                this.previousElement.nextElement = null;
            } else {
                System.out.println("Stack is empty");
                return 0;
            }
            return this.value;
        }
    }
}




class withJavasPackage {
    public static void main(String[] args) {
        Stack<Integer> stack = new Stack<>();

        stack.push(7);
        stack.push(3);
        stack.push(8);
        stack.push(2);
        System.out.println(stack.pop());
        System.out.println(stack.pop());
        stack.push(7);
        System.out.println(stack.pop());
        System.out.println(stack.pop());
    }
}