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 !!
int[] answer = new int[] { 3, 2 } List<Integer> expected = Arrays.stream(answer).boxed().collect(Collectors.toList()); Object[] objArrayOfIntArrays = new Object[] { new int[] { 1, 2 }, // add 2 new int[] { 1, 2 }, // add 2 new int[] { 3, 2 }, // query freq 2 new int[] { 2, 2 }, // delete 2 new int[] { 3, 2 }, // query freq 2 }My question is, is there a way to turn
objArrayOfIntArraystoList<List<Integer>>?Hi Tim,
Object[] objArrayOfIntArrays1 = new Object[] { new int[] { 1, 2 }, // add 2 new int[] { 1, 2 }, // add 2 new int[] { 3, 2 }, // query freq 2 new int[] { 2, 2 }, // delete 2 new int[] { 3, 2 }, // query freq 2 }; List<List<Integer>> primitiveList = Arrays .stream(objArrayOfIntArrays1) .map(q -> { return Arrays.stream((int[]) q) .boxed() .collect(Collectors.toList()); }).collect(Collectors.toList());Hope it Helps,
Praveen
Object[] objArrayOfIntArrays1 = new Object[] { new int[] { 1, 2 }, // add 2 new int[] { 1, 2 }, // add 2 new int[] { 3, 2 }, // query freq 2 new int[] { 2, 2 }, // delete 2 new int[] { 3, 2 }, // query freq 2 }; List<List<Integer>> primitiveList=Arrays.stream(objArrayOfIntArrays1) .map(q->{return Arrays.stream((int[]) q).boxed().collect(Collectors.toList());}).collect(Collectors.toList());