Problem with 'instanceof'??

Question

Hi!
I have following code:
Class[] ifs = msg.getClass().getInterfaces();
for(int i = 0; i < ifs.length;i++)
     System.out.println("msg if: " + ifs);
System.out.println("msg is SomeMessage: " + (msg instanceof my.own.services.SomeMessage));
And what I get to console is:
msg if: interface my.own.services.SomeMessage
msg is SomeMessage: false
How is this possible? First clause proves that this message 'msg' implements my own interface, but the second one does not!!??

Answer 1

I don't know Eclipse; there may be some way you could convince it to load everything with the same class loader or something. Or maybe if you add a hack that loads the message classes using the regular Java class loaders at program startup, Eclipse's loaders will use them instead of loading new copies.
A few non-Eclipse ways come to mind:
Don't use "instanceof". Instead, if you e.g. need to classify messages as "red"/"yellow"/"green", add a method getColor() into the messages. Sort of how OO is supposed to be done anyway. Requires that you can add the classification method to the topmost message superclass or interface.
Or, in a pinch, do what you do in your code above: write a function "boolean implementsInterface(Object msg, String interface_name)" using getClass().getInterfaces() and string comparison. Perhaps not terribly efficient, though, if used very often -- might take a 1/100000th of a second or something.