interface A {
   void someMethod();
}

class B implements A {
    void someMethod() {
        // implementation here
    }
}

class c implements A { //this  should not allowed in this project
}

// Hides the implementation details of ArrayList within a List variable
List<String> strs = new ArrayList<String>();
// Hides the implementation details of LinkedList within the same List variable
strs = new LinkedList<String>();
// All code using strs is agnostic to what kind of list it is (mostly)
strs.add("Hello, Dolly");
System.out.println(strs.get(0));