Stack, foreach, wrong order?

Question

When using Java's foreach syntax, Stack doesn't use LIFO ordering on the outputted elements. Consider the following code:

import java.util.Queue; import java.util.Stack; import java.util.LinkedList;  public class QueueStackTest {   private static int[] numbers = {1, 2, 3, 4, 5};    public static void main(String[] args) {     Stack<Integer> s = new Stack<Integer>();     Queue<Integer> l = new LinkedList<Integer>();      for (int i : numbers) {       s.push(i);       l.offer(i);     }      System.out.println("Stack: ");     for(Integer i : s) {       System.out.println(i);     }      System.out.println();     System.out.println("Queue:");     for(Integer i : l) {       System.out.println(i);     }   } } 

Output:

Stack:  1 2 3 4 5  Queue: 1 2 3 4 5 

Questions:

1. Does this make sense? Is it a bug?
2. Can I guarantee that this will, at least, return Queue elements in the correct order?
3. When consuming (processing) a Stack or a Queue, is this the best way to do it? Or should I make a more manual loop with something like: while(!s.isEmpty()) { handle(s.pop()); } or while(!l.isEmpty()) { handle(l.poll()); }

Answer 1

There is an interesting footnote in Stack's Javadoc:

A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. For example:

Deque stack = new ArrayDeque();

An extended version of your program:

  public static void main(String[] args) {     Stack<Integer> s = new Stack<Integer>();     Deque<Integer> d = new ArrayDeque<Integer>();     Queue<Integer> l = new LinkedList<Integer>();      for (int i : numbers) {       s.push(i);       l.offer(i);       d.push(i);     }      System.out.println("Stack: ");     for(Integer i : s) {       System.out.println(i);     }      System.out.println();     System.out.println("Queue:");     for(Integer i : l) {       System.out.println(i);     }     System.out.println();     System.out.println("Deque:");     for(Integer i : d) {       System.out.println(i);     }   }    

gives

.... Deque: 5 4 3 2 1 

So maybe switch to Deque for a more consistent behavior.