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From Andi Vajda <>
Subject Re: Some questions on implementing java interfaces
Date Sat, 19 Jan 2019 22:56:21 GMT

  Hi Petrus,

On Sat, 19 Jan 2019, Petrus Hyvönen wrote:

> I am working on wrapping a number of (java) interfaces as python classes
> (through JCC).
> Typically I have an "Interface" and make a class "PythonInterface", where I
> take the methods and make public nativec mehtods of them. In some cases my
> Interfaces has methods of same name but different parameters. What are the
> best way to implement this, how does JCC behave in those cases, would both
> "point" to the same python function. The alternative I have is to make
> separate native functions and somehow separate the names of the similar
> methods. Le me know if you have some expeience.

To "implement" a Java interface from Python you first need an extension 
point Java class that actually implements this interface.
For example, see java/org/apache/pylucene/util/
in the PyLucene sources.
It works just like a Java class you wish to "extend" from Python, you first 
need an extension point Java class that actually extends the class.

If you have overloads of Java methods (ie, methods with the same name but 
different parameters) you should provide Java implementations that call a 
different native method, with a particular name, for each overload 
signature. For example, the remove() method in 
java/org/apache/pylucene/util/ defines two native methods, 
removeAt(int) and removeObject(Object) that are called by Java
implementations (or overrides) of the remove(int) and remove(Object) 
methods defined on java.util.List, respectively.

> My second questions is on default implementation in interfaces. Some of the
> default methods in the interface are unlikely to be needed to reimplement.
> I have so far however put all methods as public native in the wrapping
> class. It seems like it is possible to call the default code from python by
> calling the interface directly "Interface.method(self, param)" and reducing
> the effort needed on the python side. Any thoughts on this?

Interface default methods are like static methods on Java classes, they 
should get wrapped by JCC just the same. If you have no reason to override 
them from Python, don't add a native "implementation".


> Thankful for any feedback,
> Regards
> /Petrus
> -- 
> _____________________________________________
> Petrus Hyvönen, Uppsala, Sweden
> Mobile Phone/SMS:+46 73 803 19 00
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