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Thread: Generics and Reflection

  1. #1
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    Default Generics and Reflection

    i've been trying to create a generic who's type is defined at runtime but so far have failed, what I want to do is something like this
    public void define(object obj){
        Class c = obj.getClass();
        List<c> list = new ArrayList<c>;
    I know the above does not compile, but so far is the best example of what I want to do, first of all question is, is this even possible? if so, how do you assign a generic its type through reflection?
    Last edited by helloworld922; March 11th, 2010 at 11:43 AM.

  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Generics and Reflection

    As far as I'm aware, generics are resolved at compile-time, so they can't be changed once your program is compiled. What you can do is use a super class for the generic parameter, and then any inheriting classes can be added to your List via polymorphism.
    Last edited by helloworld922; March 11th, 2010 at 11:48 AM.

  3. #3
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    Default Re: Generics and Reflection

    I was fearing that was the only way, since I wanted to create a simple DAO object (Using hibernateTemplates from spring) that would save,update,delete,getAll and getById procedure since so far I have seen the only thing that changes is the Type of object they receive, Thanks for the answer and should I find out any work afound to this I'll post it here.
    oh and Now that thas has come up, if I send an object of Type X (X being any used defined class) hidden behind an object due to polymorfism, will it still find the right type of class to be mapped? the following code should illustrate this.

    User us = new User("username","password");
    Object obj = (Object) us;

    The above implies the hbm.xml file or annotation are correct. would that work and save the user? or an object of any other class for that matter?

  4. #4
    Super Moderator Json's Avatar
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    Default Re: Generics and Reflection

    Lists are just lists, you can put whatever you want into them, generics is an extension to the collection interfaces which lets you have type safety at compile time.

    Just do something like this.

    List list = new ArrayList();

    Now you can shove whatever objects in there you want and if you really need it to use generics you can just do something like this.

    List<Object> list = new ArrayList<Object>();

    // Json

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