What's the difference between HashSet and Set?

Question

Saw the code snippet like

Set instances = new HashSet();

I am wondering if Hashset is a special kind of set. A

Answer 1

The HashSet is an implementation of a Set.

Answer 2

Set is a collection that contains no duplicate elements. Set is an interface.

HashSet implements the Set interface, backed by a hash table (actually a HashMap instance).

Since HashSet is one of the specific implementations of Set interface.

ASet can be any of following since it was implemented by below classes

ConcurrentSkipListSet : A scalable concurrent NavigableSet implementation based on a ConcurrentSkipListMap. The elements of the set are kept sorted according to their natural ordering, or by a Comparator provided at set creation time, depending on which constructor is used.

CopyOnWriteArraySet : A Set that uses an internal CopyOnWriteArrayList for all of its operations.

EnumSet : A specialized Set implementation for use with enum types. All of the elements in an enum set must come from a single enum type that is specified, explicitly or implicitly, when the set is created.

TreeSet :A NavigableSet implementation based on a TreeMap. The elements are ordered using their natural ordering, or by a Comparator provided at set creation time, depending on which constructor is used.

LinkedHashSet: ash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries.

But HashSet can be only LinkedHashSet since LinkedHashSet subclasses HashSet

Answer 3

Set is a parent interface of all set classes like TreeSet, LinkedHashSet etc.

HashSet is a class implementing Set interface.

Answer 4

HashSet is a class derived from Set interface. As a derived class of Set, the HashSet attains the properties of Set. Important and the most frequently used derived classes of Set are HashSet and TreeSet.

Answer 5

Set is the general interface to a set-like collection, while HashSet is a specific implementation of the Set interface (which uses hash codes, hence the name).

Answer 6

**

• Set:

** It is an interface which is a subtype of Collection interface, just like LIST and QUEUE.

Set has below 3 subclasses, it is used to store multiple objects without duplicates.

1. HashSet
2. LinkedHashSet
3. TreeSet(which implements SortedSet interface)

**

• HashSet:

**

Can use one NULL value(as Duplicate is not allowed), data is stored randomly as it does not maintain sequence.