Extending ArrayList of classes implementing certain classes containing generics doesn't work?

Question

Someone knows why this doesn't work?

public class ArrayList<E extends EXTDBinterface<T>> 
    extends java.util.ArrayList<E> implements List<E>,
    RandomAccess, Cloneable, java.io.Serializable {}

Eclipse complains about T not being resolved to a type... Is it impossible to extend the ArrayList class for types extending EXTDBinterface<T>? The point is I would like to use T inside the class, but sadly only this works:

public class ArrayList<E extends EXTDBinterface> 
    extends java.util.ArrayList<E> implements List<E>,
    RandomAccess, Cloneable, java.io.Serializable {}

but then how to get the generic type T of EXTDBinterface at runtime...?

bellum · Accepted Answer · 2013-01-09 09:58:18Z

3

First doesn't work cause you didn't set type T. Also you don't need to extend and implement all stuff again cause ArrayList has had this yet. Write, for example:

class ArrayList<T,E extends EXTDBinterface<T>> 
extends java.util.ArrayList<E>{}

answered Jan 9, 2013 at 9:58

bellum

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1 Comment

reverse_engineer Over a year ago

Yes thanks for the additional correction of removing the implements! This is the correct answer, but don't know if you or GanGnaMStYleOverFlowErroR was first ^^

Brian Agnew · Accepted Answer · 2013-01-09 09:51:53Z

0

how to get the generic type T of EXTDBinterface at runtime

You can't do that given that Java makes use of type erasure. If you need the actual type, then you'll have to pass that in (normally as a Class-typed parameter)

answered Jan 9, 2013 at 9:51

Brian Agnew

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2 Comments

reverse_engineer Over a year ago

Thank you for your answer. Sadly, I think you're right... Checking out crazy solutions here ^^. None seem to work...

reverse_engineer Over a year ago

Check out bellum's answer. Seems to do what I want!

PermGenError · Accepted Answer · 2013-01-09 09:57:55Z

0

You have to define T as the type argument for the class

public class ArrayList<T, E extends EXTDBinterface<T>> 
    extends java.util.ArrayList<E> implements List<E>,
    RandomAccess, Cloneable, java.io.Serializable {}

edited Jan 9, 2013 at 9:57

answered Jan 9, 2013 at 9:52

PermGenError

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3 Comments

reverse_engineer Over a year ago

Thank you for your answer. Eclipse complains even more with this ^^. But would it compile?

PermGenError Over a year ago

umm, i compiled fine for me, what does eclipse complain about ?

reverse_engineer Over a year ago

Thank you for your answer. Yes, after your edit it works! But did you edit before or after bellum's answer? Cause it says 43 minutes both ^^

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