Is it possible to create object using two Generics in Java?

Question

I want to define instance variables using two Generics like below.

class Foo<S,T>{
     private S<T> Boo ;
     .
     .
}

public class Test{
     public static void main(String[] args){
          Foo<ArrayList, String> foo = new Foo<ArrayList, String>();          

    }
}

But It doesn't work... Is it kinda wrong grammar? I really need to this kind of grammar.

Answer 1

This is invalid syntax

S<T>

because for any x<T>, x must be a known class or interface type.

What you want is a container type and an element type. This is possible

class Foo<C extends Collection<E>, E>{
    private C boo;

...

Foo<ArrayList<String>, String> foo = new Foo<>();

Answer 2

Maybe you need:

class Foo<S>{
     private S Boo ;
     .
     .
}

public class Test{
     public static void main(String[] args){
          Foo<ArrayList<String>> foo = new Foo<ArrayList<String>>();          

    }
}