Effective Java

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ITEM 52: USE OVERLOADING JUDICIOUSLY
243
difference because all overloadings of 
println
return 
void
, so the method
reference couldn’t possibly be a 
Callable
. This makes perfect sense, but it’s not
the way the overload resolution algorithm works. Perhaps equally surprising is
that the 
submit
method invocation would be legal if the 
println
method weren’t
also overloaded. It is the combination of the overloading of the referenced method
(
println
) and the invoked method (
submit
) that prevents the overload resolution
algorithm from behaving as you’d expect.
Technically speaking, the problem is that 
System.out::println
is an 
inexact
method reference 
[JLS, 15.13.1] and that “certain argument expressions that
contain implicitly typed lambda expressions or inexact method references are
ignored by the applicability tests, because their meaning cannot be determined
until a target type is selected [JLS, 15.12.2].” Don’t worry if you don’t understand
this passage; it is aimed at compiler writers. The key point is that overloading
methods or constructors with different functional interfaces in the same argument
position causes confusion. Therefore,