EnumSet : copyOf ( Collection c)

public static <E extends Enum<E>> EnumSet<E> copyOf(Collection<E> c)

Creates an enum set initialized from the specified collection.

import java.util.*;

class EnumSetCopyOfCollection{
 enum Day{
  MON,TUE,WED,THU,
  FRI,SAT,SUN;
 }
 
 public static void main(String args[]){
  Collection<Day> coll1 = new ArrayList<> ();
  
  /* Add Elements to the Collection */
  coll1.add(Day.MON);
  coll1.add(Day.TUE);
  coll1.add(Day.WED);
  coll1.add(Day.THU);
  coll1.add(Day.FRI);
  
  EnumSet<Day> mySet1 = EnumSet.copyOf(coll1);
  
  System.out.println("Elements in coll1 are");
  System.out.println(coll1);
  
  System.out.println("Elements in mySet1 are");
  System.out.println(mySet1);
 }
}

Output

Elements in coll1 are
[MON, TUE, WED, THU, FRI]
Elements in mySet1 are
[MON, TUE, WED, THU, FRI]

1. throws IllegalArgumentException if c is not an EnumSet instance and contains no elements

import java.util.*;

class EnumSetCopyOfCollectionIllegal{
 enum Day{
  MON,TUE,WED,THU,
  FRI,SAT,SUN;
 }
 
 public static void main(String args[]){
  Collection<Day> coll1 = new ArrayList<> ();
  
  EnumSet<Day> mySet1 = EnumSet.copyOf(coll1);
  
  System.out.println("Elements in coll1 are");
  System.out.println(coll1);
  
  System.out.println("Elements in mySet1 are");
  System.out.println(mySet1);
 }
}

Output

Exception in thread "main" java.lang.IllegalArgumentException: Collection is empty
        at java.util.EnumSet.copyOf(EnumSet.java:166)
        at EnumSetCopyOfCollectionIllegal.main(EnumSetCopyOfCollectionIllegal.java:12)

 2. throws NullPointerException if c is null

import java.util.*;

class EnumSetCopyOfCollectionNull{
 enum Day{
  MON,TUE,WED,THU,
  FRI,SAT,SUN;
 }
 
 public static void main(String args[]){
  Collection<Day> coll1 = null;
  
  EnumSet<Day> mySet1 = EnumSet.copyOf(coll1);
 }
}

Output

Exception in thread "main" java.lang.NullPointerException
        at java.util.EnumSet.copyOf(EnumSet.java:165)
        at EnumSetCopyOfCollectionNull.main(EnumSetCopyOfCollectionNull.java:12)

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