TreeSet vs HashSet vs LinkedHashSet

The post here nicely summarized the collections TreeSet, HashSet, and LinkedHashSet in Java. I mostly repeat that.

TreeSet	HashSet	LinkedHashSet
public class TreeSet extends AbstractSet implements SortedSet, Cloneable, Serializable	public class HashSet extends AbstractSet implements Set, Cloneable, Serializable	public class LinkedHashSet extends HashSet implements Set, Cloneable, Serializable
unique values	unique values	unique values
red-black tree	hash table	hash table with double links
ascending order	undefined order	insertion order
$O(\log n)$ for add, remove and contains	$O(1)$	$O(1)$, a littler slower than HashSet except for the operation of iteration

For more details, please see the reference blog.

References:

Vidya's Blog