Set

Set Interface also extends the Collection Interface. Set mean that it does not allow duplicate element i.e it care about uniqueness. There are three classes that implements Set interface

  • HashSet
  • TreeSet
  • LinkedHashSet
Difference between HashSet, TreeSet and LinkedHashSet
HashSet TreeSet LinkedHashSet
A HashSet is unsorted, unordered, no duplicates. A TreeSet is sorted and no duplicates. It is an Ordered version of HashSet and no duplicates.
Inherit from set. Inherit from SortedSet Inherit from set.
It is heterogeneous. It is homogeneous. It is heterogeneous.

Syntax of ArrayList, Vector and LinkedList :
Set Create Add Traverse
HashSet HashSet name=new HashSet(); name.add("name1"); name.add("name2"); Iterator i =name.iterator();
TreeSet TreeSet name=new TreeSet(5); name.add("name1"); name.add("name2"); Iterator i =name.iterator();
LinkedHashSet LinkedHashSet name=new LinkedHashSet(5); name.add("name1"); name.add("name2"); Iterator i =name.iterator();
Example to show HashSet insertion : 
import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;
public class HashSetDemo {
	String name;
	String address;
	Integer id;
	public HashSetDemo(String name, String address,Integer id)
	{
		this.name=name;
		this.address=address;
		this.id=id;
	}
	public String toString()
	{
		return "name ="+name+" address = "+" id = "+id; 
	}
	public static void main(String[] args) {
		HashSetDemo hsd1=new HashSetDemo("Peter","USA",1001);
		HashSetDemo hsd2=new HashSetDemo("James","UK",1002);
		HashSetDemo hsd3=new HashSetDemo("Tim","Australia",2000);
		Set hash=new HashSet();
		hash.add(hsd1);
		hash.add(hsd2);
		hash.add(hsd3);
		hash.add(hsd4);
		System.out.println(hash);
	}
}