Lets discuss some methods commonly used with Sets in java

• addAll is used to add one set to another

      union.addAll(cubes); //where union and cubes are 2 two 
  

• retainAll is used to find common elements between two sets ``` intersection.retainAll(cubes);

  So above we have intersection as one set and cubes as another and above command will create  a new Set which will contain only the elements 
   that were common between two sets. Please note retainAll is a destructive operation so new Set will only contain common elements and original 
  intersection set will be lost
  

• Passing String literal to a Set - We can't add elements to a Set all at once(i.e using a String literal) so we can first create a String to an array based
  on spaces and then convert that array to ArrayList and then pass that list to Set using addAll

  String sentence = "A day in the life of programmer";
   String[] arrayWords = sentence.split(" ");
   words.addAll(Arrays.asList(arrayWords)); //words is a Set
  

• removeAll gives the asymmetric difference i.e creates a new Set that contains all elements in SetA but removes all elements from SetB that were also present in SetB.And it is a destructive operation i.e it changes SetB so better to copy SetB to new Set as we have done in diff2 below

 Set<String> diff2 = new HashSet<>(SetA);
 diff2.removeAll(SetB);

• Symmetric Set-There is no way in Java to get a Set of elements that were not common in two Sets i.e if SetA contains a,b,c and SetB contains b,d,e then create a Set that only contains a,d,e i.e leave the common element b

But instead there is a workaround. Create a union of two Sets using addAll.And then create a Set that only contains common elements and then remove common elements from the union.

     Set<String> unionTest = new HashSet<>(SetA);
     unionTest.addAll(SetB);

     System.out.println("===========Intersection================");
     Set<String> intersectionTest  = new HashSet<>(SetA);
     intersectionTest.retainAll(SetB);

     System.out.println("===========symmetric diff================");
     unionTest.removeAll(intersectionTest);

• And then to check if one set is subset of another we use containsAll , but this method is a non destructive i.e it just returns true or false but does not create a new Set

   if(SetA.containsAll(intersectionTest)){
      System.out.println("intersectionTest is subset of SetA");
    }