A Queue using a stack. This uses an additional stack from the stack memory through recursion.

QueueFromStack

import java.util.Stack;

public class QueueFromStack<E> {

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

    public void push(E element) {
        if (this.stack.empty()) {
            this.stack.push(element);
        } else {
            E e = this.stack.pop();
            this.push(element);
            this.stack.push(e);
        }
    }

    public E pop() {
        if (!this.stack.empty()) {
            return this.stack.pop();
        } else {
            return null;
        }
    }

    public static void main(String[] args) {
        QueueFromStack<String> queue = new QueueFromStack<String>();
        queue.push("A");
        queue.push("B");
        queue.push("C");
        queue.push("D");
        queue.push("E");
        System.out.println(queue.pop());
        System.out.println(queue.pop());
        System.out.println(queue.pop());
        System.out.println(queue.pop());
        System.out.println(queue.pop());
    }
}