Why should we declare interface methods as public?

java interface public-method
Vishnu picture Vishnu · Mar 8, 2012 · Viewed 31.4k times · Source

When I implement an interface method, I am forced to make it a public method.

We may have cases where we want to use either the default (like in case of access within the same package) or protected.

Can anyone please explain the reason behind this limitation?

Answer

Péter Török picture Péter Török · Mar 8, 2012

Interfaces are meant to define the public API of a type - and only that, not its implementation. So any method (or static member) you define in an interface is by definition public.

Since an interface can't contain any concrete implementation, there is no way to call any member methods from within. And declaring such methods but leaving the calls to them to subclasses or totally unrelated clients would mean your type definition is incomplete and brittle. That is why if you need to define protected or package access members, you can do so in an abstract class (which may also contain implementation).

Related questions

Should methods in a Java interface be declared with or without a public access modifier?

Should methods in a Java interface be declared with or without the public access modifier? Technically it doesn't matter, of course. A class method that implements an interface is always public. But what is a better convention? Java itself is …

Read More
Implements vs extends: When to use? What's the difference?

Please explain in an easy to understand language or a link to some article.

Read More
How should I have explained the difference between an Interface and an Abstract class?

In one of my interviews, I have been asked to explain the difference between an Interface and an Abstract class. Here's my response: Methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can …

Read More