Is it possible to find an instance of an object without it being passed to

Question

Hi all,
I have a parser class "MessageParser" which i pass a message which is of type "String" to it for it to be parsed. The parsing method signature for the class is
public void parse(String message);
I need to pass an instance of "Properties" to it but i dont want to change the signature of the method to add a new argument to it. I have been struggling with this for the last couple of days and have tried a couple of options - see http://stackoverflow.com/questions/5134462/sending-in-an-object-of-type-object-instead-of-string-polymorphism
The class that calls the parsing method "ParserManager" knows of the properties object. Is there a way for the MessageParser to find the properties object without it being passed to it?
Thanks
ps - also posted in http://stackoverflow.com/questions/5140795/is-it-possible-to-find-an-instance-of-an-object-without-it-being-passed-to-the-me

Answer 1

ziggy wrote:
I need to pass an instance of "Properties" to it but i dont want to change the signature of the method to add a new argument to it. I have been struggling with this for the last couple of days and have tried a couple of options - see http://stackoverflow.com/questions/5134462/sending-in-an-object-of-type-object-instead-of-string-polymorphism
The class that calls the parsing method "ParserManager" knows of the properties object. Is there a way for the MessageParser to find the properties object without it being passed to it?I completely agree with Kayaman if you can get away with only the passing the Properties once (as he suggests, at construction time).
If you can't (ie, you must pass the Properties with each message), then I suspect you have a new type of Parser, and your design will have to reflect that.
One possibility would be to extend Parser with a PropertiesParser interface that defines a new parse() method and either update the current ParserManager to "understand" the difference, or create a new one.
The problem with the first option is that the manager then becomes a dispatcher, which kind of goes against the grain of OO programming (what if you need to add a third type of parser, or a fourth?).
Another possibility (probably better) would be to create a variant of your MessageObject class that includes Properties, and a variant of your MessageCParser that knows how to deal with such an object.
There are many ways to go, and only you probably know which is best.
That said, if you can get away with passing the Properties once, definitely follow Kayaman's advice.
Winston