java-collection: HashSet also returns ascending order then why TreeSet?

Hashset doesn´t guarantee the order of elements. But it calculates hashcode for objects in it. You might be having it since integers might be giving a sequential hashcode (until the capacity max is reached)

Hashset has an array of buckets. According to source code initial capacity is 16:

static final int DEFAULT_INITIAL_CAPACITY = 16;

So when you try your small integers they got placed up in order.

if you try below:


Set<Integer> intSet=new HashSet<Integer>();
intSet.add(1);
intSet.add(21);
intSet.add(2);
intSet.add(22);
intSet.add(7);
intSet.add(3);
intSet.add(4);
intSet.add(9);
intSet.add(1);
intSet.add(13);
for(Integer i:intSet){
System.out.println(i);
}

It will not maintain ascending order and insertion order either. HashSet is faster than TreeSet so if you don´t want to maintain the order then go for HashSet.