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Thread: Generics and Dynamic Instantiation Problem

  1. #1
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    Question Generics and Dynamic Instantiation Problem

    Can anyone help me to fix the code in the Main so that is works as intended?
    Gurus will know what I'm after.

    Please see below:

    public abstract class MyBaseElement 
    public class MyElementA extends MyBaseElement
    public class MyElementB extends MyBaseElement
    public class MyElementC extends MyBaseElement
    public interface Mapper<T>
    public class MyMapperA implements MyMapper<MyElementA>
    public class MyMapperB implements MyMapper<MyElementB>
    public class MyMapperC implements MyMapper<MyElementC>

    // this method returns an instance of
    // one of the child classes: MyElementA, MyElementB, MyElementC, etc...

    public MyBaseElement getSpecificElement() {...}

    // this method returns a specific mapper based on the element
    public Mapper<? extends MyBaseElement> getSpecificMapper(MyBaseElement element)
        if (element instanceof MyElementA) return new MyMapperA;
        if (element instanceof MyElementB) return new MyMapperB;
        if (element instanceof MyElementC) return new MyMapperC;

    // Main
    MyBaseElement element = getSpecificElement();
    // the line below compile
    Class<? extends MyBaseElement> myElement = element ;
    //the line below does not compile: can not convert from MyBaseElement to Mapper<? extends MyBaseElement>
    // Any ideas, please?
    Mapper<? extends MyBaseElement> myMapper = getSpecificMapper(myElement ) 
    // end-Main

  2. #2
    mmm.. coffee JavaPF's Avatar
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    Default Re: Generics and Dynamic Instantiation Problem

    Quote Originally Posted by marcosmarcos
    Can anyone help me to fix the code in the Main so that is works as intended?
    Gurus will know what I'm after.
    I have no idea what you are after.

    Firstly I would recommend posting something we can compile.
    Secondly, please give us an indepth description of your problem.
    Please use [highlight=Java] code [/highlight] tags when posting your code.
    Forum Tip: Add to peoples reputation by clicking the button on their useful posts.

  3. #3
    Super Moderator Json's Avatar
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    Default Re: Generics and Dynamic Instantiation Problem

    I agree with JavaPF here, somewhat confusion this.

    However, I'm not sure this will work, into the method getSpecificMapper you're passing in a Class<? extends MyBaseElement> but in the method signature it takes a MyBaseElement, not a Class.

    // Json

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