java - Callable as Functional Interface with lambdas -

java - Callable<Void> as Functional Interface with lambdas -

i learning new java8 features. , here question:

why not allowed utilize callable<void> functional interface lambda expressions? (compiler complains returning value) , still legal utilize callable<integer> there. here sample code:

public class test { public static void main(string[] args) throws exception { // works fine testint(() -> { system.out.println("from testint method"); homecoming 1; }); testvoid(() -> { system.out.println("from testvoid method"); // error! can't homecoming void? }); } public static void testint(callable<integer> callable) throws exception { callable.call(); } public static void testvoid(callable<void> callable) throws exception { callable.call(); } }

how explain behavior?

for void method (different void method), have homecoming null.

void placeholder stating don't have homecoming value (even though build -- callable here -- needs one). compiler not treat in special way, still have set in "normal" homecoming statement yourself.

java lambda java-8 void callable