Dynamic inheritance: wouldn't it be useful sometimes?

Question

Hey, you ever have this problem?
You are holding a reference to an object of some class that was given to you by an external source. However you'd like to override one of the methods to do something else, and then perhaps call the original method. Wouldn't it be nice if you could somehow dynamically inherit from an already existing object.
An example might be, you get a ldap DirContext object from somewhere, It's possible under some circumstance you don't want to close it. What you'd like to do is override close, and possibly call the original objects close depending on some setting.
I realize the answer is 'use aggregation', not inheritance, but that can be a royal pain if the base object has alot of methods.
Hmm, maybe that's what java.lang.reflect.proxy is all about....
anyone?

Answer 1

Ok, first i agree with what you are saying (all), i'm just not happy about it. Here's an example.
I've got a class that provides an LDap DirContext, through a "get" type method. Sometimes I'd like this class to maintain a persistent connection to the ldap server (through this DirContext) other times I wan't the connection to be recreated each time. Either way, the user uses the same interface to get this objects so:
interface LDAPProvider
DirContext getDirectoryContext();
When it's in persistent mode, it just returns a member variable, when not it creates a new one.
Well, I certainly don't want the user calling close on this returned object, as it may be that i'm maintaining a persistent connection. I also do want them to call close in the case that it is not a persistent connection.
So, i do
interface MyLDAPProvider
DirContext getDirectoryContext();
void releaseDirectoryContext( DirContext ctx );
and hope the user calls my method and not close... Which is just plain ugly and dangerous.
Alternately i create a DirContext implementing object (luckily i can cause this is an interface, what to do if this is a class that's final) and use aggregation, and implement all the DirContext methods, yuck, just to get the one close behavior. Also oogley
I really just want to do, (get out the mallots)
ctx.extendInterface( new DirContext()
private MyLDAPProvider lp = getTheAboveProviderSomeHow();
public void close()
if (!lp.isPersistent())
super.close();
}