In Java, a boxed stream is a stream of the wrapper class instances to simulate a stream of primitives.
1. What is a Boxed Stream?
Java Stream API has been designed to work with objects, similar to Collections API. Streams do not treat the primitive types the same as objects.
In Stream API, a stream of primitives can be represented by the following 3 classes:
IntStreamLongStreamDoubleStream
To convert from a stream of primitives to a stream of objects, these classes provide boxed() method that returns a Stream consisting of the elements of the given stream, each boxed to an object of the corresponding wrapper class.
Stream<Integer> stream = IntStream.of(1, 2, 3, 4, 5).boxed();
Stream<Long> stream1 = LongStream.of(1, 2, 3, 4, 5).boxed();
Stream<Double> stream2 = DoubleStream.of(1.0, 2.0, 3.0, 4.0, 5.0).boxed();2. Need of Boxed Streams
Without boxing the stream items, we cannot perform the regular stream operations on them. For example, we cannot collect the int values to a list, directly.
//Compilation issue
/*List<Integer> list = IntStream.of(1,2,3,4,5)
.collect(Collectors.toList());*/To make the above collecting process work, we must box the stream items first.
//Works fine
List<Integer> list = IntStream.of(1,2,3,4,5)
.boxed()
.collect(Collectors.toList());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());