Set interface

This is another core interface in the java collection hierarchy. The special thing is Set cannot contain duplicates. The set has three main implements.

1. java.util.TreeSet
2. java.util.HashSet
3. java.util.LinekedHashSet

Common characteristics

• No duplicates
• Not thread-safe

Other characteristics

• HashSet is the fastest set implementation, TreeSet is the slowest one.
• HashSet doesn't maintain order. But LinkedHashSet maintains insertion order while TreeSet maintains sorted order because it implements a sortedSet interface.
• Both HashSet and LinkedHashSet allow null values, but TreeSet doesn't allow null values.
• LinkedHashSet was introduced in 1.4 version in Java.

TreeSet vs HashSet vs LinkedHashSet

Look at the following example to understand Treeset. It shows about sorting of the TreeSet. 

import java.util.Set;
import java.util.TreeSet;

public class TreeSetDemo {

   public static void main(String[] args) {
  
       Set<Integer> treeSet = new TreeSet<>();
  
       treeSet.add(30);
       treeSet.add(10);
       treeSet.add(50);
       System.out.println(treeSet);
   } 
}

Look at the following example to get a brief idea about the set interface.

import java.util.Set;
import java.util.TreeSet;

public class TreeSetDemo {

   public static void main(String[] args) {
  
       Set<Integer> treeSet = new TreeSet<>();

  
       treeSet.add(30);
       treeSet.add(10);
       treeSet.add(50);
       System.out.println(treeSet);
  
       System.out.println(treeSet.size());
       System.out.println(treeSet.isEmpty());
       System.out.println(treeSet.contains(500));
       System.out.println(treeSet.remove(10));
       System.out.println(treeSet.equals(50));
       treeSet.clear();
       System.out.println(treeSet);
   }
}

Look at the following example to get an idea about the things that you can do with sets. The following example shows to get distinct characters.

import java.util.Set;
import java.util.TreeSet;

public class TreeSetDemo {

   public static void main(String[] args) {
  
       Set set = new TreeSet<>();
  
       String s = "This is a set interface";
       String []arr = s.split("");
  
       for(String i : arr){
           set.add(i);
       }
  
       System.out.println(set);
   }
}