midy62 midy62 - 1 month ago 15
Java Question

method reference vs lambda expression

I want to replace lambda expression by method reference in the below example :

public class Example {

public static void main(String[] args) {
List<String> words = Arrays.asList("toto.", "titi.", "other");
//lambda expression in the filter (predicate)
words.stream().filter(s -> s.endsWith(".")).forEach(System.out::println);
}
}


I want to write a something like this :

words.stream().filter(s::endsWith(".")).forEach(System.out::println);


is it possible to transform any lambda expression to method reference.

Answer

There is no way “to transform any lambda expression to method reference”, but you can implement a factory for a particular target type, if this serves recurring needs:

public static <A,B> Predicate<A> bind2nd(BiPredicate<A,B> p, B b) {
    return a -> p.test(a, b);
}

with this, you can write

words.stream().filter(bind2nd(String::endsWith, ".")).forEach(System.out::println);

but actually, there’s no advantage. Technically, a lambda expression does exactly what you want, there’s the minimum necessary argument transformation code, expressed as the lambda expression’s body, compiled into a synthetic method and a method reference to that synthetic code. The syntax
s -> s.endsWith(".") also is already the smallest syntax possible to express that intent. I doubt that you can find a smaller construct that would still be compatible with the rest of the Java programming language.

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