EnumSet : complementOf

public static <E extends Enum<E>> EnumSet<E> complementOf (EnumSet<E> s)

Creates an enum set with the same element type as the specified enum set, initially containing all the elements of this type that are not contained in the specified set.

import java.util.*;

class EnumSetComplementOf{
 enum Day{
  MON,
  TUE,
  WED,
  THU,
  FRI,
  SAT,
  SUN;
 }
 
 public static void main(String args[]){
  EnumSet<Day> mySet1 = EnumSet.of(Day.MON, Day.TUE);
  EnumSet<Day> mySet2 = EnumSet.complementOf(mySet1);
  
  System.out.println("Elements in mySet1 are");
  System.out.println(mySet1);
  
  System.out.println("Elements in mySet2 are");
  System.out.println(mySet2);
 }
}

Output

Elements in mySet1 are
[MON, TUE]
Elements in mySet2 are
[WED, THU, FRI, SAT, SUN]

1. throws NullPointerException if s is null

import java.util.*;

class EnumSetComplementOfNull{
 enum Day{
  MON,
  TUE,
  WED,
  THU,
  FRI,
  SAT,
  SUN;
 }
 
 public static void main(String args[]){
  EnumSet<Day> mySet = EnumSet.complementOf(null);
 }
}

Output

Exception in thread "main" java.lang.NullPointerException
        at java.util.EnumSet.copyOf(EnumSet.java:146)
        at java.util.EnumSet.complementOf(EnumSet.java:185)
        at EnumSetComplementOfNull.main(EnumSetComplementOfNull.java:15)

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