Is there a default variable placeholder for lambdas in java8?

Question

Is there a default variable placeholder for lambdas in java8, like _ for scala?

Here is scala example:

case class Person(name:String, age:Int)
val people = List(Person("Jack", 35), Person("Arjun", 16), Person("Sasha", 13), Person("Sara", 8))
val teens = people.filter(_.age >= 13).filter(_.age <= 19)

Assuming there is a Person class defined, here is java example:

List<Person> people = Arrays.asList(new Person("Jack", 35), new Person("Arjun", 16), new Person("Sasha", 13), new Person("Sara", 8));
List<Person> teens = people.stream()
                           .filter(p -> (p.getAge() >= 13 && p.getAge() <= 19))
                           .collect(Collectors.toList());

Is there a way to write the filter in last line without defining variable p. Obviously this is not a big issue, but just curious. I also understand that I could write a method in Person class like isTeenager and pass that to lambda, but that's not the point either. Just want to know if there is a default variable placeholder for lambdas in java8.

Answer 1

It's been proposed and rejected:

wunderbars were considered and (overwhelmingly) rejected by the EG.

Answer 2

There isn't, no. You could use a method reference to make it a bit closer; for that you would define a boolean method isATeen(Person p) and then do something like this:

List<Person> teens = people.stream()
                       .filter(Person::isATeen)
                       .collect(Collectors.toList());

(Assuming that you defined the method is defined in Person. You could define it elsewhere.)

That way you don't have to explicitly create a name for the instance of Person in the filter. You do of course do so in the method, so it's not much better.

UPDATE: With JEP 302, Phase 2 in JDK 9 the underscore has actually become an illegal name for a variable in any position. That way, future Java versions may use _ as a default placeholder for lambdas in a similar way to languages such as Scala. Or they may use it differently or not at all. We'll have to wait an see.