is the type of System.out.println functional interface?

Question

I do not understand one thing, should not the type of the method reference be a functional interface? So how do we pass System.out::println as a parameter to forEach?in the following code :

1-is System.out::println a Consumer?

2-if yes what is its generic type? I do not mean the type of list that is calling the method, but the generic type of the method reference that passed to the forEach.

Consumer<Integer> consumer=System.out::println;
numbers.forEach(consumer); 

Answer 1

This part of code:

Consumer<Integer> consumer=System.out::println;

is equal to this lambda expression:

Consumer<Integer> consumer=i->System.out.println(i);

and above code block could be written in this way as an anonymous inner class using Consumer interface:

Consumer<Integer> consumer=new Consumer<Integer>(){
   public void accept(Integer i){
      System.out.println(i);
   }
}

So "System.out.println" itself it is not a functional interface, but when you use :: you implicitly implement the Consumer interface.