Issue with Java 8 Lambda for effective final while incrementing counts

Question

I want to use Java 8 Lambda expression in following scenario but I am getting Local variable fooCount defined in an enclosing scope must be final or effectively final.

Answer 1

There is a count method in stream to do counts for you.

long fooCount = map.keySet().stream().filter(k -> k.contains("FOO")).count();
long barCount = map.size() - fooCount;

If you want parallelisation, change .stream() to .parallelStream().

Alternatively, if you were trying to increment a variable manually, and use stream parallelisation, then you would want to use something like AtomicLong for thread safety. A simple variable, even if the compiler allowed it, would not be thread-safe.