CODEWITHSUNDEEP
javainheritanceinterface
Matt_DontKnow
Matt_DontKnow

Reputation: 49

Extend interface with defined fields?

I've got a question for you? As we all know, interface fields in Java are default public, static and final as well. How about extending interfaces? For example if we have some interface with defined fields in it and we create another interface which extends interface with fields, we shouldn't be able to inherit fields, because they are literally static and also final. But we can! So could you explain it to me why?

interface interfaceWithFields{
String name = "Matthew";}

interface interfaceWithoutFields extends interfaceWithFields{}

And when we call standard output method, it will return Matthew:

System.out.println(interfaceWithoutFields.name); //no problem at all

Thanks in advance for responses. It's late at night and I might have confused something.

Upvotes: 0

Views: 734

Answers (2)

Radiodef
Radiodef

Reputation: 37845

This is normal. Subclasses and subinterfaces in general inherit static members from their supertypes.*

9.2:

The interface inherits, from the interfaces it extends, all members of those interfaces, except for fields, classes, and interfaces that it hides; abstract or default methods that it overrides (§9.4.1); and static methods.

The wording there is kind of, umm wordy, but it says interfaces inherit static fields from superinterfaces unless they are not hidden. (Hiding is when you declare a variable with the same name.)

In practice, the compiler will just replace interfaceWithoutFields.name with interfaceWithFields.name. There is only one static variable name exists.

* (Except, weirdly, static methods are not inherited from superinterfaces.)

Upvotes: 4

Brian Thorpe
Brian Thorpe

Reputation: 327

I'm not sure if this the technical answer, but in this case it works very similar to how a normal class would work. If you inherit from a Base class with a public, static, or final field, it will also be in the extended class. So at least in that sense it seems reasonable that interfaces would in a similar manner.

Upvotes: 1

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