[rhm54]

Thanks for your help! The variables not being intialized and the null comparison were at fault. Now I seem to have a logic problem that I cannot wrap my head around. The problem appears to be in the push method. I push on 5 numbers 1, 2, 3, 4, 5 in that order so when I pop() them I should get 5, 4, 3, 2, 1 however I get this instead:

1
5
3
2
The stack is empty, nothing to return
0

Here is the code:

Code:

package com.shadowconcept.mcdougal;

import java.util.*;

public class StackImplementationUsingTwoQueues {

	Queue<Integer> q1 = new LinkedList<Integer>();
	Queue<Integer> q2 = new LinkedList<Integer>();
	
	public int pop() {
		if (q1.peek() == null) {
			System.out.println("The stack is empty, nothing to return");
			int i = 0;
			return i;
		}
		else {
			int pop = q1.remove();
			return pop;
		}
	}
	
	public void push(int data){
		if (q1.peek() == null){
			q1.add(data);
		}
		else {
			for (int i = 0; i < q1.size(); i++){
				q2.add(q1.remove());
			}
			q1.add(data);
			for (int j = 0; j < q2.size(); j++){
				q1.add(q2.remove());
			}
		}	
	}
	
	public int top(){
		if (q1.peek() == null){
			int temp = 0;
			System.out.println("The Stack is empty returning value 0");
			return temp;
		}
		return q1.peek();
	}
	
	public int size(){
		return q1.size();
		}
 	
	public static void main(String[] args) {
		StackImplementationUsingTwoQueues s1 = new StackImplementationUsingTwoQueues();
		s1.push(1);
		s1.push(2);
		s1.push(3);
		s1.push(4);
		s1.push(5);
		System.out.println(s1.pop());
		System.out.println(s1.pop());
		System.out.println(s1.pop());
		System.out.println(s1.pop());
		System.out.println(s1.pop());
		}

}