Java 解析点标识符

Question

What are the rules Java uses to resolve dotted identifiers?

For example:

import Foo.Bar;

class Foo
{
    public static class Bar
    {
    };
};

Now, Foo.Bar can refer to either the imported class Bar or the one defined in the source code. How is this kind of ambiguity resolved?

I have tried this one case so I know what happens in practice, but I'm looking for more than that; I want to know the underlying rules. For example, if Foo.Bar exists in the source file, can I still refer to the imported class Foo.Bar.Baz ? What if Foo.Bar is a package and also a class? If the compiler can't find Foo.Bar in the closest Foo , does it just give up, or does it keep looking for other Foo s until it either runs out or finds one that matches?

(Incidentally, I have found the relevant bit in the language specification. It doesn't help much...)

Answer 1

To resolve a weird clash like this, the java compiler follows the same rules it uses to resolve things like local variable names clashing with instance field names - it uses the "nearest" declaration. In this case, the local class Foo will win over the imported one.

A clash can also happen when two classes of the same name is being imported. The most common example is java.util.Date and java.sql.Date . If you have imported them both into your class, you must refer to them using their fully qualified name.