| Re: Class Warfare [message #40392] |
Fri, 06 August 2004 00:07 |
Michael Wallace
Messages: 409
Registered: December 2003
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Senior Member |
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> Here's an example... First create a Java string.
>
> IDL> session = Obj_New('IDLjavaObject$IDLJAVABRIDGESESSION')
> IDL> jstring = Obj_New('IDLjavaObject$java_lang_String', $
> 'java.lang.String', 'My String')
>
> OBJ_ISA will tell you that it is a string, but doesn't tell you that it
> is also an Object even though java.lang.String directly inherits from
> java.lang.Object.
>
> IDL> print, Obj_Isa(jstring, 'IDLjavaObject$java_lang_String')
> 1
> IDL> print, Obj_Isa(jstring, 'IDLjavaObject$java_lang_Object')
> 0
I don't know if anyone else is interested in this stuff, but I've
learned another interesting IDL-ism. Just thought I'd pass it on just
in case there are other Java programmers besides me out here.
It looks like I was expecting way too much out of Obj_Isa(). Obj_Isa()
doesn't really do much of anything with Java objects. When a Java
object gets created, the part of the name following 'IDLjavaObject$'
appears to be purely arbitrary. I can enter any string I want to in
that area, and it's the string that Obj_Isa() appears to use for the
so-called instanceof operator.
; Create a Java string, but give a random string for the object name
IDL> jstring = Obj_New('IDLjavaObject$java_lang_Foo', $
'java.lang.String', 'My String')
; Obj_Isa() is matching the string provided...
IDL> print, Obj_Isa(jstring, 'IDLjavaObject$java_lang_Foo')
1
; And Obj_Isa() doesn't match the actual type of the class!
IDL> print, Obj_Isa(jstring, 'IDLjavaObject$java_lang_String')
0
So, the answer to my original question is to give an appropriate name to
my objects when I create them. If I will only be used an interface of a
specific object, I can create the name to match the interface name and
viola! Obj_Isa() will return what I expect. The only limitation is that
for each object created, you can only choose one class or interface. I
still think a true instanceof operator needs to exist. I'd rather
handle class typing problems by checking instanceof beforehand rather
than relying on the error handler to tell me I have a type problem.
-Mike
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