Jaap Coomans Jaap Coomans - 5 months ago 20
Java Question

How to determine the class of a generic type?

I'm creating a generic class and in one of the methods I need to know the Class of the generic type currently in use. The reason is that one of the method's I call expects this as an argument.

Example:

public class MyGenericClass<T> {
public void doSomething() {
// Snip...
// Call to a 3rd party lib
T bean = (T)someObject.create(T.class);
// Snip...
}
}


Clearly the example above doesn't work and results in the following error: Illegal class literal for the type parameter T.

My question is: does someone know a good alternative or workaround for this?

Answer

Still the same problems : Generic informations are erased at runtime, it cannot be recovered. A workaround is to pass the class T in parameter of a static method :

public class MyGenericClass<T> {

    private final Class<T> clazz;

    public static <U> MyGenericClass<U> createMyGeneric(Class<U> clazz) {
        return new MyGenericClass<U>(clazz);
    }

    protected MyGenericClass(Class<T> clazz) {
        this.clazz = clazz;
    }

    public void doSomething() {
        T instance = clazz.newInstance();
    }
}

It's ugly, but it works.