Accessing a parameter in subclasses

Question

Currently I have something like this:
public abstract class AbstractData<E extends Entity> {
    protected Class<E> clazz;
    public void process()
     System.out.println("I am processing " + clazz);
public class Data extends AbstractData<Product> {
    protected Class clazz = Product.class;
}I works but there must be a more concise and less error prone way to do the same thing.
More specifically, I would rather initialize the clazz field in the AbstractData super class.
Is it possible?
Thanks.
Oscar

Answer 1

First of all, your code is not doing what you think it does. The 'clazz' in the subclass 'hides' the existing 'clazz' field the AbstractData class. Run this, for example:
import java.util.*;
class Entity { }
class Product extends Entity { }
abstract class AbstractData<E extends Entity> {
     protected Class<E> clazz;
     public void process1() {
          System.out.println("I am processing " + clazz);
class Data extends AbstractData<Product> {
     protected Class clazz = Product.class;
     public void process2() {
          System.out.println("I am processing " + clazz);
public class Test {
     public static void main(String[] args) {
          Data d = new Data();
          Class<Product> clazzInAbstractData = ((AbstractData<Product>)d).clazz;
          System.out.println(clazzInAbstractData);
          d.process1();
          Class clazzInData = d.clazz;
          System.out.println(clazzInData);
          d.process2();
/* outputs:
class Product
I am processing class Product
null
I am processing null
*/Perhaps instead ofclass Data extends AbstractData<Product> {
     protected Class clazz = Product.class;
}, you want class Data extends AbstractData<Product> {
     { clazz = Product.class; }
}, or if you want to extra clear and explicit about what's happening, class Data extends AbstractData<Product> {
     { super.clazz = Product.class; }
}