Methods visibility in interface

Question

Do all methods in an Interface has by default Public visibility mode?

Answer 1

Just to add to other answers here: all methods are public, however, if the interface itself is package-local then effectively all methods are also package-local.

You can therefore mix public and package-local methods, by making a package-local interface extend a public one.

public interface P{
  void iAmPublic();
}

interface L extends P{
  void iAmPackageLocal();
}

Here L effectively has one public and one package-local method. Clients from outside the package will only see iAmPublic(), whereas ones from inside the package will see both methods.

In the same way you can nest interfaces inside other classes to achieve even tighter method visibility.