Java Boxed Stream Example

In Java 8, if you want to convert stream of objects to collection, then you can use one of the static methods in the Collectors class.

//It works perfect !!
List<String> strings = Stream.of("how", "to", "do", "in", "java")
    				.collect(Collectors.toList());

The same process doesn’t work on streams of primitives, however.

//Compilation Error !!
IntStream.of(1,2,3,4,5)
    .collect(Collectors.toList());

To convert a stream of primitives, you must first box the elements in their wrapper class and then collect them. This type of stream in called boxed stream.

1. IntStream – stream of ints

Example to convert int stream to List of Integers.

//Get the collection and later convert to stream to process elements
List<Integer> ints = IntStream.of(1,2,3,4,5)
				.boxed()
				.collect(Collectors.toList());
		
System.out.println(ints);

//Stream operations directly
Optional<Integer> max = IntStream.of(1,2,3,4,5)
				.boxed()
				.max(Integer::compareTo);

System.out.println(max);

Program Output:

[1, 2, 3, 4, 5]
5

2. LongStream – stream of longs

Example to convert long stream to List of Longs.

List<Long> longs = LongStream.of(1l,2l,3l,4l,5l)
				.boxed()
				.collect(Collectors.toList());
		
System.out.println(longs);

Output:

[1, 2, 3, 4, 5]

3. DoubleStream – stream of doubles

Example to convert double stream to List of Doubles.

List<Double> doubles = DoubleStream.of(1d,2d,3d,4d,5d)
				.boxed()
				.collect(Collectors.toList());
		
System.out.println(doubles);

Output:

[1.0, 2.0, 3.0, 4.0, 5.0]

Drop me your questions in comments section related to boxed streams or stream of primitives in Java Stream API.

Happy Learning !!