Monkey patching a Java class?

[A. Sundararajan]

Agree. I'll fix the wiki.

Thanks
-Sundar

On Monday 21 July 2014 06:17 PM, Marc Downie wrote:
> Got it, thanks. I'd consider adding a sentence to the "Java.extend" docs (
> https://wiki.openjdk.java.net/display/Nashorn/Nashorn+extensions) to that
> end.
>
> My outside perspective is that it's unexpected that a) you can't, b) trying
> to fails silently, and c) setting arbitrary members on Java.extend classes
> work but they simply disappear never to return.
>
> best,
>
> Marc
>
>
> On Mon, Jul 21, 2014 at 6:07 AM, A. Sundararajan <
> sundararajan.athijegannathan at oracle.com> wrote:
>
>> No, you can't add new methods to extended class (no facility to declare
>> types and so on) - only overrides of super class methods.
>>
>> -Sundar
>>
>>
>> On Sunday 20 July 2014 10:28 PM, Marc Downie wrote:
>>
>>> Does adding new methods to Java.extend based subclasses actually work?
>>> Currently I have (staying close to the example code):
>>>
>>> var ArrayList = Java.type("java.util.ArrayList")
>>> var ArrayListExtender = Java.extend(ArrayList)
>>> var printSizeInvokedArrayList = new ArrayListExtender() {
>>>       size: function() { print("size invoked!"); },
>>>     banana: function() { print("Banana"); } // this doesn't override
>>> anything
>>> in ArrayList
>>> }
>>>
>>> printSizeInvokedArrayList.size() // WORKS
>>> printSizeInvokedArrayList.banana() // TYPE ERROR ([] has no such function
>>> "banana")
>>>
>>> // and even:
>>>
>>> printSizeInvokedArrayList.peach = function(){print("Peach");} // no
>>> error,
>>> but....
>>> printSizeInvokedArrayList.peach() // TYPE ERROR ([] has no such function
>>> "peach")
>>>
>>> (1.9.0-ea-b23 and 1.8.0_20-ea-b23)
>>>
>>> Marc.
>>>
>>>
>>>
>>> On Thu, May 1, 2014 at 11:23 PM, A. Sundararajan <
>>> sundararajan.athijegannathan at oracle.com> wrote:
>>>
>>>   No, you can't add/remove a method (or public field) of a Java class to
>>>> use
>>>> within the script. You could subclass and expose that subclass as
>>>> "java.io.File" by
>>>>
>>>>       var oldFile = java.io.File;
>>>>       java.io.File = Java.extend(oldFile, ...)
>>>>
>>>> But, I'd not recommend it - besides user can still get original
>>>> java.io.File via Java.type (unless you do similar hack on Java.type as
>>>> well!!)
>>>>
>>>> Cleaner approach is to expose a script API wrapping java.io.File.
>>>>
>>>> -Sundar
>>>>
>>>>
>>>> On Thursday 17 April 2014 12:03 AM, HRJet wrote:
>>>>
>>>>   Is it possible to monkey patch a Java class for use within Javascript?
>>>>> For example, I want to add a convenience method to java.io.File class,
>>>>> say
>>>>> "readAsString()".
>>>>>
>>>>> Then, in javascript I want to call file.readAsString()  where file is an
>>>>> instance of java.io.File. Note that the file instance may be created by
>>>>> some third-party code, over which I have no control.
>>>>>
>>>>> In Java land, this seems to be usually done with CGLib or AspectJ, etc.
>>>>>
>>>>> I was wondering if nashorn had some trick up its sleeve for doing this
>>>>> in
>>>>> script land, since this sort of thing is common in Javascript.
>>>>>
>>>>> thanks,
>>>>> HRJ
>>>>>
>>>>>