[leftover] Using _ as a variable

[Remi Forax]

If someone try to use '_' as a variable, javac reports the following error,
which is not very readable.

javac -source 10 LambdaLeftovers.java 
LambdaLeftovers.java:10: error: as of release 10, '_' may only be used as an identifier of:
      System.out.println(_);
                         ^
  unused lambda, method, or catch formal parameter.
1 error

what about 
  as of release 10, '_' can only be used as an unused formal parameter.

cheers,
Rémi