Generic methods to refactor code

[Remedy]

Hello,
I have a little problem with the use of generic methods to refactor code. I actually trying to instantiate an object in a generic method as follows:

private <X extends A> X instanciationSelective(boolean Class) {
  X = anObject null;          
  if (Class)
    anObject = new Has();
  else
    anObject = new B();
  return anObject
}

with class B inherits class A. Obviously I'll give you a thousand, the compiler can not dip that anObject is an instance of A or its sub-classes and I released two best big error "incompatible types" (found A required X and B found required X ). If I cast upon instantiation, then I am entitled to the usual warning "unchecked cast". How to get out of there without error or warning ? Why in the methods generic substitution is not made (as in a generic class, any object type X has access to methods defined in A)?

[Praetor]

Hello,
The problem:
1) You do not set X. Apart from knowing that extends A, we know nothing.
2) nothing is known of X, and you try to assign an instance of A.
3) nothing is known of X, we know nothing of B, and you try to assign an instance of A.
The solution:

private A instanciationSelective(boolean Class) {
  A = anObject null;          
  if (Class)
    anObject = new Has();
  else
    anObject = new B();
  return anObject;
}

Yes, generics are not necessary in this case.

[Remedy]

Hello,
It's normal that I do not define X as it is a generic.
code of A and B in this example is very simple:
class A ()
class B extends A ()

Yes, generics are not necessary in this case

If still the problem with your solution is that the declared type of the instance returned will always be A and can not use the behavior of B without cast (the purpose of using generic types is precisely to avoid cast, thus avoiding any time to check the type of execution. Other ideas (if possible with generics unless another solution could be as clean)?

[Praetor]

Hello
Thank you, I still know what a generic. The only possible solution then is to pass the class instead of a boolean as a parameter:

private <X extends A> X instanciationSelective (Class <X> class)
  throws InstantiationException, IllegalAccessException
{
  return class.newInstance();
}

No feasible alternative, generic or not.

[Remedy]

Hello,
It's still amazing even when there is no alternative ... in addition, is con of using the class loader to do that because the compiler has even less control over the thing ... I feel it's going to the old caster. Yet it was a classic application of generic types. By the way thanks for your help. And if you have any alternative then please do post back.

[MindSpace]

Hello,

Yet it was a classic application of generic types ...

No, your code is not at all type-safe.
You have a statement like this:
private <X extends A> X instanciationSelective(boolean Class)
And code like this:

B temp1 = instanciationSelective(true);
B temp2 = instanciationSelective(false);

The compiler has no way to check the return type of method because it depends on a boolean. It should be an analysis code to verify that this is not the compiler (and it might not necessarily do anyway). Explains a bit more what you do because it must surely be another solution. Also if you do the hard cast as using two different method (the sample instanciationSelective () that you show does not interest).