Question about Reflection

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isamura - 18 Oct 2005 07:00 GMT

I was wondering if I am using Reflection in a way that was not intended...or not possible.

I want to store a class, MyClass0 in a variable:
Class cls = Class.forName("MyClass0");

Later I want to instantiate a new instance from 'cls':

MyClass0 inst;
Constructor cons = cls.getConstructor(new Class[]);
inst = cons.newInstance(new Object[]);
...

This is fine so far. But what if I have several classes: MyClass1, MyClass2.
I also want to reuse the above code to create new instances of these classes.

The problem is in the variable declaration statement:
MyClass0 inst;

The type could be any of the three classes. Obviously
cls inst;
won't compile.

Alternatively,
Object inst;
Constructor cons = cls.getConstructor(new Class[]);
inst = cons.newInstance(new Object[]);
produces type mismatch compiler error.

I tried to cast the instance creation:
inst = (cls)cons.newInstance(new Object[]);
but that didn't work either. Perhaps I am missing something.

So what else is possible, besides forgetting code reuse in this situation? <g>

Thanks!

.K

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Alexey_Volynskyy - 18 Oct 2005 08:27 GMT

> I was wondering if I am using Reflection in a way that was not intended...or not possible.
>
[quoted text clipped - 31 lines]
>
> Thanks!

Do this way:

> Class cls = Class.forName("MyClass0"); //This is correct.

Object inst ;
inst = cls.newInstance(); //calls constructor without parameters

If you want to call specific contructor, you can get all contructors
available:

Constructor[] constrs = cls.getContructors();

Then select needed constructor and call it:
Object inst1 = constrs[0].newInstance(Object[] initArgs);

BR
Alexey

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Roedy Green - 18 Oct 2005 09:07 GMT

>So what else is possible, besides forgetting code reuse in this situation? <g>

All your classes could implement the same interface.
All could derive from the same base.
You do call all the methods via reflection and just call the instances
Objects.

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Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.

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isamura - 18 Oct 2005 18:52 GMT

: >So what else is possible, besides forgetting code reuse in this situation? <g>
:
: All your classes could implement the same interface.
: All could derive from the same base.
: You do call all the methods via reflection and just call the instances
: Objects.

Jollygood! My classes do use the same base (same inheritance hierarchy) but the key was a common
interface.

I did thought about using more reflection but decided against it for code maintenance reasons.

The code compiles now. Let's see if it runs <g>

Thanks again for your helpful input.

Cheers!

.K

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Question about Reflection

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