use generic type as class

[Leandro Coutinho]

hello!

public class Dao<T> {

	private Session session;
	private Class persistentClass;
	
	public Dao(Class persistentClass) {
		this.session = HibernateUtil.currentSession();
		this.persistentClass = persistentClass;		
	}
...
// instantiating the class
Dao<Student> daoStudent = new Dao<Student>(Student.class);

I would like to be able to instantiate the class, without the needing to pass a parameter. I think that maybe it is possible, because T represent this class.
Something like this:

public class Dao<T> {

	private Session session;
	private Class persistentClass;
	
	public Dao() {
		this.session = HibernateUtil.currentSession();
		this.persistentClass = T;		
	}
...

Is there a way to do this?

[Ninad Kulkarni]

Leandro
Please give details so that we understand your question.
I have seen your code but code will not compile.

[Jesper de Jong]

No, you cannot do that the way you proposed. Generics in Java have certain limitations, one of them is that you can't instantiate an object from a generic type with for example "new T()". Probably that's the reason why your class needs the Class parameter - so that it can create new instances of that class with: persistentClass.newInstance().

If you want to know all the details of Java generics and why "new T()" doesn't work, see Angelika Langer's Java Generics FAQ.

(The reason why new T() doesn't work is because of type erasure - see this from that FAQ for more info).

[Leandro Coutinho]

Thank you!

Great link.