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Miguel Gonzalez Rocha2,849 Points
What are interfaces and superinterfaces?
He made a new List, arraylist and after that i got confused because i investigated "Collections" and it says it is a superinterface (List belongs to Collection), then how could he use it without making it in the first place? or you dont need to "make" a new Collection because it is a Superinterface, and is like using String which everyone has access to it?
Allan Clark10,810 Points
An interface is like a guarantee that your class will implement certain methods. ArrayList extends the List interface, this just means that an ArrayList will have all the methods that are required to be a List. In the real world if you think the Door concept as being an interface, you know anything that "extends" door (i.e. front door, car door, doggie door) will work a certain way.
Superinterface is not a separate entity, it refers to the hierarchy. When an interface is extended or implemented it becomes a Superinterface of what extended/implemented it. If class C implements interface B, and interface B extends interface A, then A is a Superinterface to B and . Also B is a Superinterface for C.
interface A (Superinterface to B and C) | interface B (Superinterface to C) | class C
*side note interface B is a Subinterface to interface A.
Collection refers a group of specific classes and interfaces that hold "collections" of objects. For example ArrayList class and Set interface are a part of Java Collections Framework (JCF) often referred to as just "collections."
Hope this helps!