Difference Between HashSet VS LinkedHashSet VS TreeSet In Java

HashSet VS TreeSet Java: In this article, we will compare important implementation classes of Set i.e.; HashSet v/s LinkedHashSet v/s TreeSet

So lets us discuss in tabular format;

HashSet VS TreeSet VS LinkedHashSet In Java

 HashSetLinkedHashSetTreeSet
Uses a hash table to store element/objects where duplicates are NOT allowedUses a combination of (hash table + LinkedList) to store element/objects where duplicates are NOT allowedUses the balanced tree to store element/objects where duplicates are NOT allowed
Insertion order is not maintained, as it uses a hashing technique to store element/objectsInsertion order is maintained, as it uses the doubly-linked list to store element/objectsInsertion order is not maintained, as element/objects are stored according to some sorting order
HashSet doesn’t deal with  sorting order, but it can be converted to TreeSet to store element/objects in some sorting orderTreeSet ts = new TreeSet(HashSet);LinkedHashSet doesn’t deal with  sorting order; but it can be converted to TreeSet to store element/objects in some sorting orderTreeSet ts = new TreeSet(linkedHashSet);Element/objects stored in TreeSet are according to some sorting order; it could be either default natural sorting order or programmer-defined customized sorting order
While iterating HashSet, we will get items in random orderWhile iterating LinkedHashSet, we will get items as per insertion orderWhile iterating TreeSet, we will get items in sorted order;  either natural ordering or customized sorting order
This is introduced in the original collection framework in Java 1.2 versionThis is introduced in Java 1.4versionThis is also introduced in the original collection framework in Java 1.2 version
Allows NULL insertion but a maximum of only one NULL valueAllows NULL insertion but a maximum of only one NULL valueFrom Java 1.7 version, NULL is not allowed to insert; But with Java version less than 1.6, only as 1st element allowed
Difference Between HashSet VS LinkedHashSet VS TreeSet In Java 1

Factors to consider while discussing any collection class

We should consider factors while discussing any implementation class of collection framework or for that matter Map interface,

  • Underlying data structure
  • Duplicates are allowed or Not
  • Insertion order is maintained or Not
  • Whether NULL insertion is possible or Not
  • If possible, how many NULL values can be inserted
  • Whether collection class provide sorting, by default
  • Is there any way to apply customized sorting
  • Performance, while dealing with retrieval or manipulation (addition/deletion)
  • By default, all methods are synchronized or Not

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