Process adjacent overlapping pairs from the java stream
I am working on a problem that I need to process overlapping pairs from the stream.
for example, consider the list → ["lion","fox","hare","carrot"] . So output will be
lion eats fox
fox eats hare
hare eats carrot.
Output items are always one less than that of the original list. I am currently using java 8 . here’s my code
Code
static <T,R> Function <T, Stream<R>> pairMap(BiFunction<T,T,R> mapper) { return new Function<> () { T previous = null; boolean hasPrevious; public Stream<R> apply(T t) { Stream<R> result; if(!hasPrevious) { hasPrevious = true; result = Stream.empty(); } else { result = Stream.of(mapper.apply(previous, t)); } previous = t; return result; } }; } static <T> Stream<T> getAdjecentOverlappingStream(List<T> list) { return list.stream().flatMap(pairMap((a,b) -> a+" eats "+ b)); } Calling method
//consider the class name I am working with is StreamUtils. StreamUtils.getAdjecentOverlappingStream(Arrays.asList("lion","fox","hare","carrot")) .forEach(System.out::println);; But this code giving me error as error: cannot infer type arguments for Function<T,R>
See full error.
Error
StreamLecture.java:83: error: cannot infer type arguments for Function<T,R> return new Function<> () { ^ reason: cannot use '<>' with anonymous inner classes where T,R are type-variables: T extends Object declared in interface Function R extends Object declared in interface Function StreamLecture.java:106: error: incompatible types: inference variable R#1 has incompatible bounds return list.stream().flatMap(pairMap((a,b) -> a+" eats "+ b)); ^ equality constraints: T#2 lower bounds: String,R#2 where R#1,T#1,T#2,R#2,T#3 are type-variables: R#1 extends Object declared in method <R#1>flatMap(Function<? super T#1,? extends Stream<? extends R#1>>) T#1 extends Object declared in interface Stream T#2 extends Object declared in method <T#2>getAdjecentOverlappingStream(List<T#2>) R#2 extends Object declared in method <T#3,R#2>pairMap(BiFunction<T#3,T#3,R#2>) T#3 extends Object declared in method <T#3,R#2>pairMap(BiFunction<T#3,T#3,R#2>) Note: StreamLecture.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 2 errors Please help me fix this error. thanks ✌
