Which Data Structure Is Used by Set in Java?


Larry Thompson

In Java, the Set interface is a part of the Java Collections Framework and is used to represent a collection of unique elements. It does not allow duplicate values and provides various methods for performing set operations such as union, intersection, and difference.

Which Data Structure Does Set Use?

The actual data structure used by the Set interface in Java depends on the specific implementation class chosen. There are several classes that implement the Set interface, including HashSet, TreeSet, and LinkedHashSet. Each of these classes uses a different underlying data structure to store the elements.


The HashSet class implements the Set interface using a hash table. It uses hashing to store elements and provides constant-time performance for basic operations like add, remove, contains, and size. However, it does not guarantee any specific order of iteration.


The TreeSet class implements the NavigableSet interface and internally uses a self-balancing binary search tree called a Red-Black tree. This data structure ensures that the elements are stored in sorted order based on their natural ordering or a custom comparator. As a result, operations like add, remove, contains are performed in O(log n) time complexity.


The LinkedHashSet class extends the HashSet class and maintains a doubly-linked list of elements in addition to a hash table. This allows it to preserve the insertion order of elements while still providing constant-time performance for basic operations.

Choosing the Right Set Implementation:

When using the Set interface in your Java program, it is important to choose the right implementation class based on your specific requirements. Here are a few considerations:

  • Performance: If you need fast access times and do not require any specific ordering of elements, HashSet is usually the best choice. It provides constant-time performance for add, remove, contains operations.
  • Natural Ordering: If you need the elements to be stored in sorted order according to their natural ordering or a custom comparator, then TreeSet should be used.
  • Maintaining Insertion Order: If you want to preserve the order in which elements were added to the set, use LinkedHashSet. It provides an efficient way to iterate over the elements in insertion order.

In conclusion, the choice of data structure depends on your specific requirements when using a Set in Java. Understanding the differences between implementations like HashSet, TreeSet, and LinkedHashSet will help you make an informed decision based on the specific needs of your application.

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