Ordering in HashSet

[Ganesha Kumar]

Hi
I read in K&B book that HashSet does not maintain the order of elements. But I have the following program:

public class ListClass {
public static void main(String[] args){
Set set = new HashSet();
set.add("Hari");
set.add("Ganesh");
set.add("Giri");
set.add("Garry");
for(int i=0;i<30;i++){
for(Object o:set){
System.out.print(o+" ");
}
System.out.println("");
}
set.add("Latha");
set.add("Zeta");
set.add("Narayan");
for(int i=0;i<30;i++){
for(Object o:set){
System.out.print(o+" ");
}
System.out.println("");
}
}
}
which produces the same output over and over again. Can anyone please explain why this is so?

[kurt hanni]

i dont know the explanation for this. but what you see is still an unordered iteration of the elements, it just happens to come out the same when there are few elements in the set.

try adding more elements(100 or more) the unordered iteration will be more obvious.

[Jesper de Jong]

The concept of a Set is that it is a collection of objects without any ordering. You can see it as a bag of objects, and the objects are all jumbled together in the bag. There is no inherent order.

This does not mean that a certain implementation of Set (such as HashSet) can't store objects in a certain order. The thing you have to keep in mind that nothing is specified or guaranteed about the order, so you should not write a program that relies on the order of objects in a HashSet.

So, the fact that a Set has no order does not necessarily mean that the objects have to be presented in a random order.

[Vipin Das]

Why are you using this statement ?
for(int i=0;i<30;i++){
The statement for(Object o:set){ itself will print the contents of the hashset.

[Jesper de Jong]

Originally posted by Vipin Das:
Why are you using this statement ?
for(int i=0;i<30;i++){
The statement for(Object o:set){ itself will print the contents of the hashset.

Probably because he wants to demonstrate that if he prints the contents of the HashSet 30 times, he gets the same ordering of the elements each time.

As I said, there's nothing wrong with that; there is no requirement anywhere that the elements have to be in a different, random order each time.

[Raghavan Muthu]

Yes. That's very true Jesper.

All what it says is "Set does NOT maintain any order". That does NOT mean that always it has to produce the results in a different order!.

The order of insertion is also one of the random orders!

[Ganesha Kumar]

Thanks for your replies