Name: laC46010 Date: 12/21/99



The JLS, p. 8.4.3.1 requires to report compile-time error for the
following example:
----------------------clss02802_b.java----------------------
 package clss02802_b;
 abstract class clss02802_a { abstract void m(); }
 public class clss02802_b extends clss02802_a { void m(){} }
----------------------clss02802.java------------------------
 package clss02802;
 import clss02802_b.clss02802_b;
 class clss02802_c extends clss02802_b {}
------------------------------------------------------------

However javac (all versions) compiles this program without complaints.
I believe it's indeed a valid Java program and p. 8.4.3.1 doesn't take
into account the case when abstract method in not inherited by
subclass.


p. 8.4.3.1 (p.158 of JLS 1st edition) reads :
    "Every subclass of A that is not abstract must provide an
    implementation for m, or a compile-time error occurs. More
    precisely, for every subclass C of the abstract class A,
    if C is not abstract, then there must be some class B such
    that all of the following are true:
  
       1) B is a superclass of C or is C itself.
       2) B is a subclass of A.
       3) B provides a declaration of the method m that is not
          abstract, and this declaration is inherited by C,
          thereby providing an implementation of method m that
          is visible to C.
    If there is no such class B, then a compile-time error
    occurs."

At the same time JLS, p. 8.2 reads :
    "Only members of a class that are declared protected or
    public are inherited by subclasses declared in a package
    other than the one in which the class is declared."
   
But in present test, the class "clss02802_c" does not inherit the
method "m" because this method belongs to a class from an another
package and has default access. So the class "clss02802_c" is a
subclass of the abstract class "clss02802_a" and there is no some class
B that "B provides a declaration of the method m that is not abstract,
and this declaration is inherited by C". Therefore compile-time error
                     ^^^^^^^^^^^^
must occur. However javac (all versions) compiles this program without
complaints.

Note that above assertion is reduced in the draft of
the JLS 2nd edition to a single sentence:
    "Every subclass of A that is not abstract must provide an
    implementation for m, or compile-time error occur."
but it still doesn't explain the discussed case.

======================================================================