How to Convert Java 8 IntStream to a List

1. Overview          

          In this tutorial, we are going to convert an IntStream to List and to an array. IntStream is a stream of primitive int values and a List is an ordered collection that holds generic values.

To convert a stream to the collection, we can call collect() method of Stream class, but this works when the streams hold non-primitive types. Calling collect() method on primitive streams give a compilation error "collect() in IntStream cannot be applied to".




2. Solutions

2.1. Call boxed() method before collecting to a List

       IntStream has a method boxed() that returns a Stream consisting of the elements each boxed to an Integer. After getting a boxed stream, we can call the collect() method to convert into a List.

Code:

package streams;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class IntStreamTest {
    public static void main(String[] args) {
        List<integer> intList = IntStream.of(10, 20, 30, 40).
                boxed().
                collect(Collectors.toList());
        System.out.println(intList);
    }
}

Result:



2.2. Call mapToObj() method before collecting to a List

       IntStream has a method mapToObj() that returns an object-valued Stream. Calling this method we can manually box the primitive integer into Integer object. After this call the collect() method to convert into a List.

Code:

package streams;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class IntStreamTest {
    public static void main(String[] args) {
        List<integer> intList = IntStream.of(10, 20, 30, 40).
                mapToObj(Integer::valueOf).
                collect(Collectors.toList());
        System.out.println(intList);
    }
}

Result:

     

3. Conclusion

    In this tutorial, we have seen 2 ways of converting an IntStream to a List using methods provided by IntStream.