I see a weird situation and wonder if I missed something. I have one class define an enum like this
public class Foo { public enum Day { Monday, Tuesday, ...}; ... } Then in another class I have
public class Bar { Foo aFoo=new Foo(); void test(){ System.out.println(Foo.Day.Monday); // ok System.out.println(aFoo.Day.Monday); // complie error Day not accessible } } Anyone have an explanation for this? Thanks.
The reason is that when you have an expression like Q.Id and Q is an expression of type T (Q is your aFoo and T = Foo):
If there is not exactly one accessible (§6.6) member of the type T that is a field named Id, then a compile-time error occurs.
In other words you can reference a static field with an instance (aFoo.someStaticVariable) but not a nested class.
So you need to use Outerclass.Nestedclass to access it.
someInstance.f, f must be a field, whether static or not - f can't be a class name. I have edited for clarity.
enum is static by default (see link in answer), that means it's the same for all instances of Foo. So it's not really useful to access it via the instance but it is useful to access it via the class itself. That's the basic idea.From the JLS §8.9:
Nested enum types are implicitly
static. It is permissible to explicitly declare a nested enum type to bestatic.
Hence it makes no sense to access Day through a Foo instance; it can only be accessed through the Foo class itself as in your first print statement.
