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Re: JNI generic type of jobject

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Daniel Pitts wrote:
>>  Philipp Kraus wrote:
>>> I use JNI calls for some Java classes. Some Java classes are generic
>>> classes like:
>>>
>>> class mytestclass<T> {
>>>
>>>   public native void mymethod();
>>>
>>> }
>>>
>>> The stub shows:
>>>
>>> JNIEXPORT void JNICALL Java_mytestclass_mymethod(JNIEnv* p_env, jobject
>>> p_object)
>>>
>>> How can I get from the jobject which object type is the generic
>>> parameter T? Because I would
>>> like to create different codes if I do something like:
>>>
>>>   mytestclass<int> x = new mytestclass<int>();
>>>   x.mymethod();
>>>
>>>   mytestclass<String> x = new mytestclass<String>();
>>>   x.mymethod();
>>
> int is not a valid generic type parameter, as int is a primitive and 
> generic types must be Object types.
> 
> Also, generics are not the same as C++ templates.  There isn't different 
> code created for each concrete usage. Its all exactly the same code.
> 
> If you are doing different behavior based on the compile time type, then 
> you need  to do a little bit more work to implement the strategy pattern.
> 
> class MyTestClass<T> {
>    private MyMethodStrategy<T> strategy;
> 
>    public mymethod() {
>       strategy.mymethod(this);
>    }
> }
> 
> interface MyMethodStrategy<T> {
>      void mymethod(MyTestClass<T> testClass);
> }
> 
> 
> class MyStringMethodStrategy implement MyMethodStrategy<String> {
>     public native void mymethod(MyTestClass<String> testClass);
> }
> 
> 
> class MyIntegerMethodStrategy implement MyMethodStrategy<Integer> {
>     public native void mymethod(MyTestClass<Integer> testClass);
> }
> 
> 
> Then you will have two different native methods to implement each strategy.

Kudos for a great answer!
+1

This pattern or ones like it are frequent and very helpful in generics programming.

-- 
Lew

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JNI generic type of jobject Philipp Kraus <philipp.kraus@flashpixx.de> - 2011-10-04 14:23 +0200
  Re: JNI generic type of jobject Silvio <silvio@moc.com> - 2011-10-04 14:28 +0200
    Re: JNI generic type of jobject Philipp Kraus <philipp.kraus@flashpixx.de> - 2011-10-04 14:49 +0200
    Re: JNI generic type of jobject Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-04 07:53 -0700
      Re: JNI generic type of jobject Philipp Kraus <philipp.kraus@flashpixx.de> - 2011-10-04 18:01 +0200
      Re: JNI generic type of jobject Lew <lewbloch@gmail.com> - 2011-10-04 12:01 -0700
        Re: JNI generic type of jobject Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-04 12:15 -0700

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