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Using covariant return type feature through ITD causes ajc to produce bad code (which then causes reflection based usages, Hibernate in my case, to produce serious errors). Here is a minimal program to reproduce the error: // Entity.java import java.io.Serializable; public interface Entity { public Long getId(); } class AnEntity implements Entity { public Long getId() { return null; } } aspect ManageEntity { declare parents: Entity implements EntityWithId; interface EntityWithId { public Serializable getId(); } } > ajc -v AspectJ Compiler DEVELOPMENT built on Friday Nov 25, 2005 at 18:17:07 GMT > ajc -1.5 Entity.java > javap AnEntity Compiled from "Entity.java" class AnEntity extends java.lang.Object implements Entity{ AnEntity(); public java.lang.Long getId(); public java.io.Serializable getId(); } Now there are two getId() methods with only return type difference, which is illegal in Java.
I'll take a look tomorrow.
Here is a pure java program: import java.io.Serializable; public interface Entity2 { public Long getId(); } class AnEntity implements Entity2,EntityWithId { public Long getId() { return null; } } interface EntityWithId { public Serializable getId(); } After compilation, if I 'javap AnEntity': class AnEntity extends java.lang.Object implements Entity2,EntityWithId{ AnEntity(); public java.lang.Long getId(); public java.io.Serializable getId(); } You can have two methods that differ purely in return type - one has to be a bridge method that forwards to the other, here is implementation of the 'Serializable getId()' method: public java.io.Serializable getId(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokevirtual #2; //Method getId:()Ljava/lang/Long; 4: areturn LineNumberTable: line 7: 0 It just calls the getId() returning a Long. AspectJ is doing the same thing. However ... there is *possibly* a bug that has concerned me for a while to do with how we tag methods as bridge methods. Either: we aren't tagging them correctly for hibernate or hibernate doesn't understand bridge methods. Ramnivas, can you try hibernate against a pure java case that results in bridge methods like the one above?
Ramnivas, have you had a chance to try hibernate on the pure Java version of this that includes bridge methods? We're in danger of missing fixing this for RC1 if there is a real problem lurking...
Good news! It is Hibernate's problem. I tried the same setup in plain Java and got identical failure. public interface SerializableEntity { public Serializable getId(); } And then public class Entity implements SerializableEntity, Serializable { private Long _id; public Long getId() { return _id; } @SuppressWarnings("unused") private void setId(Long id) { _id = id; } } Therefore, marking this bug as "INVALID". Thanks Andy for working on this. I will do more investigation and report to Hibernate.
