Creating general Lambdas with Java

In Java, you can add a type parameter to a static method to create a method that handles generics Can you do the same thing with Lambdas?

In my code, I have

final private static <K,V> supplier<Map<K,List<V>> supplier=HashMap::new;

I'm trying to make type arguments, for example, it's a function, but it won't let me

If I do this:

final private static supplier<Map<?,List<?>>> supplier=HashMap::new;

It does not accept the argument that I try to use it What can I do?

Solution

One solution might be to wrap the method reference in the method so that the target type derivation resolves the type on the calling site:

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.supplier;

public class GenericLambda
{
    // Syntactically invalid
    //final private static <K,List<V>> supplier=HashMap::new;

    final private static supplier<Map<?,List<?>>> supplier=HashMap::new;

    // A workaround
    private static <K,List<V>>> supplier()
    {
        return HashMap::new;
    }


    public static void main(String[] args)
    {
        // Does not work
        //usesupplier(supplier);

        // Works
        usesupplier(supplier());
    }

    private static <K,V> void usesupplier(supplier<Map<K,List<V>>> s)
    {
        System.out.println(s.get());
    }
}