Nullcheck method using java8 method reference possible?

Question

Due to rich profiling, our Java code is cluttered with outputs of method results of nullable objects.

It looks like this

namedObject == null ? "?" : namedObject.getName()

is it possible to write a static method for this? (e.g. looking like this):

Util.nvl( namedObject, NamedObject::getName, "?" )

What would = Util.nvl look like? I've experimented a bit an searched google but yielded no result.

This does not work:

public static <T> T nvl(T value, Function<T, ?> method, T nullSubstition) {
    return value == null ? nullSubstition : (T) method.apply(value);
}

The compiler tells me: non-static method getName() cannot be referenced from a static context

Answer 1

Your signature can't be correct. You want your method to take the NamedObject as first argument (so T is a NamedObject), and to return a String (so now T is String).

You need two generic type parameters:

public class Utils {

    public static <O, T> T nvl(O value, Function<O, T> method, T nullSubstition) {
        return value == null ? nullSubstition : method.apply(value);
    }

    static class NamedObject {
        String getName() {
            return "foo";
        }
    }

    public static void main(String[] args) {
        NamedObject foo = null;
        String name = Utils.nvl(foo, NamedObject::getName, "bar");
        System.out.println("name = " + name); // name = bar

        foo = new NamedObject();
        name = Utils.nvl(foo, NamedObject::getName, "bar");
        System.out.println("name = " + name); // name = foo
    }
}

An even better signature, allowing more flexibility, would be

public static <O, T> T nvl(O value, Function<? super O, ? extends T> method, T nullSubstition) {
    return value == null ? nullSubstition : method.apply(value);
}

Answer 2

Your method's generics aren't defined correctly. You're attempting to create a method that receives an object of a certain type (T, for argument's sake, or a NamedObject in the given example), and applies a method that returns an object of a different type (S, for argument's sake, or String in the given example), or a default S value if the passed object is null:

public static <T, S> S nvl(T value, Function<T, S> method, S nullSubstition) {
    return value == null ? nullSubstition : (S) method.apply(value);
}

Note that Java 8's Optional may allow you to write this in a more elegant way (although elegance is somewhat in the eye of the beholder):

public static <T, S> S nvl(T value, Function<T, S> method, S nullSubstition) {
    return Optional.ofNullable(value).map(method).orElse(nullSubstition);
}