Users are having lots of problems using Collections.EMPTY_LIST.
Some of these problems seem to have something to do with the compiler
behaving differently in the presence of separate compilation.
I'm not sure which of these should be allowed and which not, but
at the very least the compiler should behave the same when the
classes are compiled together as when they are compiled separately.

Offhand, I suspect there should be no hard errors here, but
I haven't studied the specification carefully to know for sure.


Here's the together case:

frog:~/workspaces/test/GenericsCollections $ cat -n EmptyList2.java
     1 class List<E> {}
     2 class Collections {
     3 static List EMPTY_LIST;
     4 }
     5 public class EmptyList2
     6 {
     7 public static void main(String[] ps)
     8 {
     9 List<String> list = Collections.EMPTY_LIST;
    10 List<String> list2 = (List<String>) Collections.EMPTY_LIST;
    11 }
    12 }
frog:~/workspaces/test/GenericsCollections $ newjavac -gj -warnunchecked EmptyList2.java
EmptyList2.java:9: warning: unchecked assignment: List to List<java.lang.String>
       List<String> list = Collections.EMPTY_LIST;
                                       ^
EmptyList2.java:10: inconvertible types
found : List
required: List<java.lang.String>
       List<String> list2 = (List<String>) Collections.EMPTY_LIST;
                                                      ^
1 error
1 warning
frog:~/workspaces/test/GenericsCollections $

Here's the separate case:

frog:~/workspaces/test/GenericsCollections $ cat -n Collections.java
     1 class Collections {
     2 static List EMPTY_LIST;
     3 }
frog:~/workspaces/test/GenericsCollections $ cat -n List.java
     1 class List<E> {}
frog:~/workspaces/test/GenericsCollections $ cat -n EmptyList.java
     1 public class EmptyList
     2 {
     3 public static void main(String[] ps)
     4 {
     5 List<String> list = Collections.EMPTY_LIST;
     6 List<String> list2 = (List<String>) Collections.EMPTY_LIST;
     7 }
     8 }
frog:~/workspaces/test/GenericsCollections $ newjavac -gj -warnunchecked List.java Collections.java
frog:~/workspaces/test/GenericsCollections $ newjavac -gj -warnunchecked EmptyList.java
EmptyList.java:5: incompatible types
found : List<E>
required: List<java.lang.String>
       List<String> list = Collections.EMPTY_LIST;
                                       ^
EmptyList.java:6: inconvertible types
found : List<E>
required: List<java.lang.String>
       List<String> list2 = (List<String>) Collections.EMPTY_LIST;
                                                      ^
2 errors
frog:~/workspaces/test/GenericsCollections $