All geek questions in one place

Java compilation error with method reference, but works with lambda

We are trying to add an overloaded method collectto our extended Java Stream API, which we currently define as:

interface ExtendedStream<R> extends Stream<R> {

   <R1> R1 collect(SerializableSupplier<Collector<? super R, ?, R1>> supplier);

}

SerializableSupplier defined as simple:

interface SerializableSupplier<T> extends Serializable, Supplier<T> {
}

Calling this collection method using lambda works fine, but calling it using a method reference has not compiled with errors such as:

Error:(50, 72) java: incompatible types: cannot infer type-variable(s) R1,capture#1 of ?,T
    (argument mismatch; bad return type in method reference
      java.util.stream.Collector<T,capture#1 of ?,java.util.List<T>> cannot be converted to java.util.stream.Collector<? super java.util.Map.Entry<java.lang.Integer,java.lang.String>,?,R1>)

I created a standalone Java class here , which you can load into your compiler to try it out.

I am currently using the Java version:

java version "1.8.0_144"
Java(TM) SE Runtime Environment (build 1.8.0_144-b01)
Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

Is this a mistake or some mistake in how we define things?

NOTE . I get this compilation error both from IntelliJ and when compiling with Maven. I do not use Eclipse.

Cheers, Galder

+4
1

javac 8, javac-9 ( ) - , .

, ... , Comparator Comparator.comparingInt...:

 return entrySet.stream().sorted(
            Comparator.comparingInt(Entry::getKey)).collect(
                    Collectors::<Map.Entry<Integer, String>> toList);
+4

Source: https://habr.com/ru/post/1685857/

More articles:


All Articles