Convert IntStream to Collection/Array

Java 8‘s Collectors class provides many static methods to collect objects from a stream and store them into collection. But these method does not work with streams of primitives.

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

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

To convert primitives stream to collection, you can adapt on of following two ways.

Using boxed streams

Using boxed() method of IntStream, LongStream or DoubleStream e.g. IntStream.boxed(), you can get stream of wrapper objects which can be collected by Collectors methods.

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

Output:

[1, 2, 3, 4, 5]

Map int to Integer

Another way is to manually to the boxing using IntStream.mapToObj(), IntStream.mapToLong() or IntStream.mapToDouble() methods. There are other similar methods in other stream classes, which you can use.

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

Output:

[1, 2, 3, 4, 5]

Convert Stream to Primitive Array

It is also useful to know how to convert primitive stream to array. Use IntStream.toArray() method to convert from int stream to array.

int[] intArray = IntStream.of(1, 2, 3, 4, 5).toArray();

System.out.println(Arrays.toString(intArray));

Output:

[1, 2, 3, 4, 5]

Similarly, use toArray() function of LongStream or DoubleStream as well.

Drop me your questions in comments section.

Happy Learning !!