Java EnumSet copyOf() Method

Description

The Java EnumSet copyOf(Collection<E> c) method creates an enum set initialized from the specified collection.

Declaration

Following is the declaration for java.util.EnumSet.copyOf() method

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

Parameters

c − the collection from which to initialize this enum set.

Return Value

This method does not return any value.

Exception

• IllegalArgumentException − if c is not an EnumSet instance and contains no elements

• NullPointerException − if c is null

Getting Copy of EnumSet Example

The following example shows the usage of Java EnumSet copyOf(Collection) method to populate the EnumSet instance. We've created a enum Numbers. Then a Collection instance is created and populated with enum values. Using copyOf(Collection) method, enumSet is populated with values of collection and resulted enumSet is printed.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Collection;
import java.util.EnumSet;

public class EnumSetDemo {

   // create an enum
   public enum Numbers {
      ONE, TWO, THREE, FOUR, FIVE
   };

   public static void main(String[] args) {

      // create a new collection
      Collection<Numbers> collection = new ArrayList<>();

      // print the collection
      System.out.println("Colletion :" + collection);

      // add two elements in the collection
      collection.add(Numbers.ONE);
      collection.add(Numbers.THREE);

      // create an EnumSet that is a copy of the collection 
      EnumSet<Numbers> set = EnumSet.copyOf(collection);

      // print the set
      System.out.println("Set:" + set);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Colletion :[]
Set:[ONE, THREE]

Getting Copy of EnumSet of Enum with Value Example

The following example shows the usage of Java EnumSet copyOf(Collection) method to populate the EnumSet instance. We've created a enum Numbers. Then a Collection instance is created and populated with enum values. Using copyOf(Collection) method, enumSet is populated with values of collection and resulted enumSet is printed.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Collection;
import java.util.EnumSet;

public class EnumSetDemo {

   // create an enum
   public enum Number {
      ONE("1"), TWO("2"), THREE("3"), FOUR("4"), FIVE("5");

      // instance variable for enum
      private String value;

      public String getValue() {
         return this.value;
      }

      // constructor should be private or protected
      private Number(String value) {
         this.value = value;
      }

      @Override
      public String toString() {
        return this.name() +"(" + this.value + ")";
      }
   };

   public static void main(String[] args) {

      // create a new collection
      Collection<Number> collection = new ArrayList<>();

      // print the collection
      System.out.println("Colletion :" + collection);

      // add two elements in the collection
      collection.add(Number.ONE);
      collection.add(Number.THREE);

      // create an EnumSet that is a copy of the collection 
      EnumSet<Number> set = EnumSet.copyOf(collection);

      // print the set
      System.out.println("Set:" + set);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Colletion :[]
Set:[ONE(1), THREE(3)]