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.

IntStream to List of Integers

Example to convert int stream to List of Integers.

List<Integer> ints = IntStream.of(1,2,3,4,5)
				.boxed()
				.collect(Collectors.toList());
		
System.out.println(ints);

Output:

[1, 2, 3, 4, 5]

LongStream to List 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]

DoubleStream to List 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.

Happy Learning !!