Java

import java.util.*;

public class S
{
	public static void main(String args[])
	{
		Set<Integer> a = new HashSet<Integer>();
		a.addAll(Arrays.asList(new Integer[] {1, 2, 3, 4}));
		System.out.println("A: "+a);

		Set<Integer> b = new HashSet<Integer>();
		b.addAll(Arrays.asList(new Integer[] {5, 2, 6, 4}));
		System.out.println("B: "+b);

		//Union
		Set<Integer> c = new HashSet<Integer>(a);
		c.addAll(b);
		System.out.println("Union: "+c);

		//Intersection
		Set<Integer> d = new HashSet<Integer>(a);
		d.retainAll(b);
		System.out.println("Intersection: "+d);

		//Difference
		Set<Integer> e = new HashSet<Integer>(a);
		e.removeAll(b);
		System.out.println("Difference: "+e);
	}
}

import java.util.*;

public class S
{
	public static void main(String args[])
	{
		SortedSet<String> s = new TreeSet<String>();

		s.add("practice");
        	s.add("geeksforgeeks");
        	s.add("quiz");
        	s.add("code");

		System.out.println(s);

		//first
		System.out.println("First: "+s.first());
		//last
		System.out.println("Last: "+s.last());

		//headSet
		System.out.println("Head: "+s.headSet("quiz"));

		//subSet
		System.out.println("Subset: "+s.subSet("code", "practice"));

		//tailSet
		System.out.println("Tail: "+s.tailSet("code"));
	}
}

import java.util.*;

public class S
{
	public static void main(String args[])
	{
		NavigableSet<Integer> s = new TreeSet<Integer>();

		//add
		for(int i = 0; i < 10; i++)
			s.add(i);

		System.out.println(s);

		//descending
		System.out.println(s.descendingSet());

		//lower
		System.out.println(s.lower(4));//3

		//floor
		System.out.println(s.floor(4));//4

		//ceiling
		System.out.println(s.ceiling(4));//4

		//higher
		System.out.println(s.higher(4));//5

		//headSet
		System.out.println(s.headSet(4));

		//subSet
		System.out.println(s.subSet(3, 8));

		//tailSet
		System.out.println(s.tailSet(4));

		//pollFirst
		System.out.println(s.pollFirst());
		System.out.println(s);

		//pollLast
		System.out.println(s.pollLast());
		System.out.println(s);
	}
}

Use a hashMap for sorting its objects, key and value have same value, complexity O(1)
Objects in hashSet are not sorted, order is based on their hash code
Not keep the insert order
NULL elements are allowed in HashSet

import java.util.*;

public class S
{
	public static void main(String args[])
	{
		Set<Integer> s = new HashSet<Integer>();
		Random r = new Random();

		//add
		s.add(r.nextInt(100));
		s.add(r.nextInt(100));
		s.add(r.nextInt(100));
		s.add(1);

		//contains
		if(s.contains(1))
			System.out.println("Contains 1 ...");

		//size
		System.out.println("Size: "+s.size());

		//remove
		s.remove(1);

		System.out.println(s);
	}
}

Maintains the insert order

import java.util.*;

public class S
{
	public static void main(String args[])
	{
		Set<Integer> a = new LinkedHashSet<Integer>();
		Random r = new Random();

		a.add(r.nextInt(100));
		a.add(r.nextInt(100));
		a.add(r.nextInt(100));
		a.add(1);
		a.add(100);
		a.add(2);

		System.out.println(a);
	}
}

Elements are sorted by key
Not keep the insert order
Allow NULL inserted
Self-balance binary tree, add, remvoe and search take O(logn) time

import java.util.*;

public class S
{
	public static void main(String args[])
	{
		Set<Integer> s = new TreeSet<Integer>();
		Random r = new Random();

		//add
		s.add(r.nextInt(100));
		s.add(r.nextInt(100));
		s.add(r.nextInt(100));
		s.add(1);
		s.add(2);
		s.add(100);

		//contains
		if(s.contains(1))
			System.out.println("Contains 1 ...");

		//size
		System.out.println("Size: "+s.size());

		//remove
		s.remove(1);

		System.out.println(s);
	}
}

All elements of each EnumSet instance must be elements of a single enum type

public enum Day
{
	Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday;
}

import java.util.*;

public class DaySet
{
	public static void main(String args[])
	{
		EnumSet<Day> s1 = EnumSet.of(Day.Monday, Day.Tuesday, Day.Sunday);

		//toString
		System.out.println(s1);

		//iterator
		Iterator itr = s1.iterator();

		while(itr.hasNext())
		{
			System.out.printf("%s\n", itr.next());
		}

		//complementOf
		EnumSet<Day> s2 = EnumSet.complementOf(s1);

		System.out.println(s2);


		//allOf
		EnumSet<Day> s3 = EnumSet.allOf(Day.class);

		System.out.println(s3);

		//range
		EnumSet<Day> s4 = EnumSet.range(Day.Monday, Day.Friday);
		System.out.println(s4);
	}
}