Set interface in Java with examples | HashSet, LinkedHashSet, TreeSet Class | SortedSet Interface

Guide to Set Interface in Java with SortedSet, HashSet, LinkedHashSet and TreeSet

Set Interface (java.util.set)

Set is part of Collection Framework. Set directly extends Collection interface and uses its capability.

Set is unordered data structure and contains only unique values means does not contains duplicate values.

Following are child classes and interfaces of Set interface :

1. HashSet Class
2. LinkedHashSet Class
3. SortedSet Interface
4. TreeSet Class

HashSet Class :

HashSet contains unordered elements and can not contains duplicate elements.

How to create new HashSet?

Set set = new HashSet()

Or

HashSet hashSet = new HashSet()

Lets see example of HashSet :

Example 1 : HashSet class demo

import java.util.HashSet;
import java.util.Set;

public class HashSetDemo {

    public static void main(String[] args) {

        Set<String> set = new HashSet<>() {{
            add("Java");
            add("Java");
            add("Python");
            add("JavaScript");
            add("C++");
            add("Php");
            add("Clanguage");
            add("DotNet");
        }};
       
        System.out.println(set);
    }
}

Output :

[Clanguage, Java, C++, JavaScript, Php, Python, DotNet]

As you can see in output, Set does not follow insertion order and contains only unique values.  

LinkedHashSet Class :

LikedHashSet maintains insertion order and contains only unique values.

Example 2 :LinkedHashSet class demo

import java.util.LinkedHashSet;
import java.util.Set;

public class HashSetDemo {

    public static void main(String[] args) {

        Set<String> set = new LinkedHashSet<String>() {{
            add("Java");
            add("Java");
            add("Python");
            add("JavaScript");
            add("C++");
            add("Php");
            add("Clanguage");
            add("DotNet");
        }};
       
        System.out.println(set);
    }
}

Output :

[Java, Python, JavaScript, C++, Php, Clanguage, DotNet]

As you can see in output LinkedHashSet maintains insertion order.

SortedSet Interface :

SortedSet interface is child of Set interface. It maintains elements in sorting (ascending) order.

As SortedSet is interface, we can not create Object of that. We need class that implements SortedSet. TreeSet class is implementation of SortedSet interface.

TreeSet Class :

TreeSet is part of Set data structure. It implements NavigableSet that extends SortedSet. Elements of the TreeSet class are stored in ascending order.

TreeSet does not allow null value.

We can also get first and last element using first() and last() method of SortedSet.

Example 3 : TreeSet class demo

import java.util.SortedSet;
import java.util.TreeSet;

public class HashSetDemo {

    public static void main(String[] args) {

        SortedSet<String> set = new TreeSet<String>() {{
            add("Java");
            add("Java");
            add("Python");
            add("JavaScript");
            add("C++");
            add("Php");
            add("Clanguage");
            add("DotNet");
        }};
       
        System.out.println(set);
        System.out.println("First element in Treeset : " +set.first()); 
        System.out.println("Last element in Treeset : " +set.last());
    }
}

Output :

[C++, Clanguage, DotNet, Java, JavaScript, Php, Python]
C++
Python

 

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