Setting the modifier 'public' in the implementation of an interface method

Question

I know that the following code is wrong because the modifier public is missed in the header of the method m1() in class B . But i wonder "Why?.". Why the code causes a compile error if public is missed.

Thanks in advance.

interface A{
  void m1();
}
class B implements A{
  void m1(){
    System.out.println("m1");
  }
}

Answer 1

By default methods have an access of package-private if no access modifier is specified, which means they are public to the package and class only. However interfaces require methods to be implemented by a class using an interface to be public.

See this stack overflow post for what default access modifiers are for classes and interfaces.