The same statement may not have multiple labels with the same name. For
example, the following program has an error:

class C {
  void f() {
    int x;
    a: a: x = 0;
  }
}

The Java compiler does not indicate this as an error.

I have already discussed this with Guy Steele who agrees that this is
an error because the statement "a: x = 0;" is considered to be nested
within the statement "a: a: x = 0;".