java.lang.reflect.Proxy and default methods

Peter Levart peter.levart at
Tue Aug 28 03:32:14 PDT 2012

On Tuesday, August 28, 2012 11:18:55 AM Peter Levart wrote:
> Currently java.lang.reflect.Proxy treats default interface methods the same
> as abstract methods (it passes their invocations to the InvocationHandler),
> which is the right thing to do if current platform interfaces like Iterator
> will have some abstract methods turned into default methods.
> But if at the same time interfaces like Iterable get new default methods,
> libraries that expose proxies to those interfaces will have to be prepared
> (modified) to handle invocations to those new methods.
> Sometimes the library writer might just want to pass default method
> invocations to the default method implementations in the interface. Will
> there be a reflection facility to call super interface methods on the proxy
> instance or is there anything else planned to facilitate this?

One way to do that without support for calling super default methods using 
reflection might be to overload java.lang.reflect.Proxy factory methods with 
variants that take additional "boolean proxyDefaultMethods" parameter so that 
when passed as "true" the proxy will act as currently (pass default method 
invocations to InvocationHandler) and when passed as "false", default methods 
in interfaces will not be "overriden" in generated Proxy class so that default 
implementations in interfaces will take over.

If someone wants to be selective (proxy some default methods and not proxy 
others), she could get the desired behaviour by creating a private sub-
interface which re-abstracts selected default methods and use the sub-
interface in the Proxy factory. The same "technique" could be used to resolve 
conflicting default methods from multiple interfaces.

Some applications that want to be more dynamic might stil prefer reflective 
access to interface super methods in the proxy...

Regards, Peter

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