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EnumSet copyOf() Method in Java

Last Updated : 02 Jul, 2018

1. The java.util.EnumSet.copyOf(Collection collect) method in Java is used to copy all of the contents from a collection to a new enum set. At first, the collection is made out of the elements of the enum and then a new enum set is created, which is the copy of the collection. Syntax:

   New_Enum_Set = EnumSet.copyOf(Collection collect)

   Parameters: The method accepts one parameter collect of the object type of the enum and refers to the collection whose values are to be copied into the New_Enum_Set. Return Values: The method does not return any values. Exceptions:
   • IllegalArgumentException : This exception is thrown if collect is not an EnumSet instance and contains elements that cannot be compared with the enum or contains no element.
   • NullPointerException : This exception is thrown if collect is NULL.
   Below program illustrates the working of java.util.EnumSet.copyOf() method: Java

   // Java program to demonstrate copyOf() method
   import java.util.*;
   
   // Creating an enum of GFG type
   enum GFG {
       Welcome,
       To,
       The,
       World,
       of,
       Geeks
   }
   ;
   
   public class Enum_Set_Demo {
   
       public static void main(String[] args)
       {
   
           // Creating an empty collection
           Collection<GFG> collect = new ArrayList<GFG>();
   
           // Adding elements to the Collection
           collect.add(GFG.Welcome);
           collect.add(GFG.World);
           collect.add(GFG.Geeks);
   
           // Displaying the collection
           System.out.println("The collection is: " + collect);
   
           EnumSet<GFG> e_set = EnumSet.copyOf(collect);
   
           // Displaying the final set
           System.out.println("The enum set is:" + e_set);
       }
   }
   

   Output:

   The collection is: [Welcome, World, Geeks]
   The enum set is:[Welcome, World, Geeks]
   

2. The java.util.EnumSet.copyOf(EnumSet e_set) method in Java is used to copy all of the contents from an existing EnumSet i.e., e_set, to a new enum set. Syntax:

   New_Enum_Set = EnumSet.copyOf(EnumSet e_set)

   Parameters: The method accepts one parameter e_set of the object type of the enum and refers to the set whose values are to be copied into the New_Enum_Set. Return Values: The method does not return any values. Exceptions: The method throws NullPointerException when e_set is NULL. Below program illustrates the working of java.util.EnumSet.copyOf() method: Java

   // Java program to demonstrate copyOf() method
   import java.util.*;
   
   // Creating an enum of CARS type
   enum CARS {
       RANGE_ROVER,
       MUSTANG,
       CAMARO,
       AUDI,
       BMW
   }
   ;
   
   public class Enum_Set_Demo {
   
       public static void main(String[] args)
       {
   
           // Creating an empty EnumSet
           // Getting all elements from CARS
           EnumSet<CARS> e_set = EnumSet.allOf(CARS.class);        
   
           // Displaying the initial EnumSet
           System.out.println("Initial set is: " + e_set);
   
           // Copying the set
           EnumSet<CARS> new_set = EnumSet.copyOf(e_set);
   
           // Displaying the final set
           System.out.println("The new set is: " + new_set);
       }
   }
   

   Output:

   Initial set is: [RANGE_ROVER, MUSTANG, CAMARO, AUDI, BMW]
   The new set is: [RANGE_ROVER, MUSTANG, CAMARO, AUDI, BMW]
   

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