A question about Generic Class.

[dmjpro]

Now a days i am looking at Generics. Which is very interesting.
But i have a confusion .......

[code=java]
class GenericClass<T> {
T obj;
GenericClass(T t){
this.obj = t;
}
}

class MyMainClass{
MyMainClass(){
GenericClass<Nu mber> gc = new GenericClass<In teger>();
}
}[/code]

Now my question is that, why it shows me error .....Compiler says that incompatible types.
But what i think as Integer extends Number .... why it's not valid please explain me!

[JosAH]

You should've used a bounded wildcard '? extends Number' for the class type
parameter and you don't have a no-arg constructor.

kind regards,

Jos

[dmjpro]

You should've used a bounded wildcard '? extends Number' for the class type
parameter and you don't have a no-arg constructor.

kind regards,

Jos

Thanks....I know i have to use bounded wildcard,But i need the clarification on it.
Actually I posted wrong.
And i think you didn't get my point.

[code=java]
class GenericClass<T> {
T obj;
GenericClass(T obj){
this.obj = obj;
}
T getObj(){return obj;}
[/code]

[code=java]
GenericClass<Nu mber> gc = new GenericClass<In teger>(100);
Number num = gc.getObj();
[/code]

Why it's not valid?

[JosAH]

Thanks....I know i have to use bounded wildcard,But i need the clarification on it.
Actually I posted wrong.
And i think you didn't get my point.

[code=java]
class GenericClass<T> {
T obj;
GenericClass(T obj){
this.obj = obj;
}
T getObj(){return obj;}
[/code]

[code=java]
GenericClass<Nu mber> gc = new GenericClass<In teger>(100);
Number num = gc.getObj();
[/code]

Why it's not valid?

No need to worry; I got your point. Think of three other classes:

[code=java]
class MeansOfTranspor tation { }
class Car extends MeansOfTranspor tation { }
class Submarine extends MeansOfTranspor tation { }
[/code]

and define a garage like this:

Garage<MeansOfTransportation> garage= new Garage<Car>();

The garage itself can store submarines, but a Garage<Car> can't. That's why
your example isn't valid. btw, I thought you were working on inner classes
and security policies or do you just hop around randomly?

kind regards,

Jos

[dmjpro]

No need to worry; I got your point. Think of three other classes:

[code=java]
class MeansOfTranspor tation { }
class Car extends MeansOfTranspor tation { }
class Submarine extends MeansOfTranspor tation { }
[/code]

and define a garage like this:

Garage<MeansOfTransportation> garage= new Garage<Car>();

The garage itself can store submarines, but a Garage<Car> can't. That's why
your example isn't valid. btw, I thought you were working on inner classes
and security policies or do you just hop around randomly?

kind regards,

Jos

lolz! Thanks Josh.
Yeah you are right ... i was learning Inner Class and Java Policies.
Inner class is so far clear but how java.policy works .... Have a look at my java policy thread..please!

Actually what I thought that
[code=java]
GenericClass<Nu mber> gc = new GenericClass<In teger>(100);
Number num = gc.getObject();
[/code]
It is type safety that's why i told due to some reasons the concepts got out.
Anyway I got your point of view.
Thanks.

[JosAH]

Anyway I got your point of view.
Thanks.

That isn't my point of view; that is how the Java language is defined.

kind regards,

Jos

[dmjpro]

That isn't my point of view; that is how the Java language is defined.

kind regards,

Jos

Everything is related to reality and you everytime make understand with real example.
And where is my policy answer .... ? :-)

[JosAH]

Everything is related to reality and you everytime make understand with real example.
And where is my policy answer .... ? :-)

I don't know; I didn't participate in that thread and I'm sure that r035198x is very
well capable to answer any reasonable question.

kind regards,

Jos