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EnumSet copyOf() Method in Java

Last Updated : 02 Jul, 2018
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  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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