QueueStack.java

package Stack;

import java.util.Queue;

public class QueueStack {
    static class Queue
{
    static Stack<Integer> s1 = new Stack<Integer>();
    static Stack<Integer> s2 = new Stack<Integer>();
 
    static void enQueue(int x)
    {
        // Move all elements from s1 to s2
        while (!s1.isEmpty())
        {
            s2.push(s1.pop());
            //s1.pop();
        }
 
        // Push item into s1
        s1.push(x);
 
        // Push everything back to s1
        while (!s2.isEmpty())
        {
            s1.push(s2.pop());
            //s2.pop();
        }
    }
 
    // Dequeue an item from the queue
    static int deQueue()
    {
        // if first stack is empty
        if (s1.isEmpty())
        {
            return -1;
        }
 
        // Return top of s1
        int x = s1.peek();
        s1.pop();
        return x;
    }
    public static void main(String[] args) {
        Queue q = new Queue();
    q.enQueue(1);
    q.enQueue(2);
    q.enQueue(3);
 
    System.out.println(q.deQueue());
    System.out.println(q.deQueue());
    System.out.println(q.deQueue());
    }
}