Generifying a class - unchecked cast

[D. Ogranos]

Hi, yet another generics question (didn't find something similar to this in the search). I have some classes which share a common pattern but make use of specific types. It appears they would be a good candidate for generifying. So far I have created a new abstract generic base class which should take most of the functionality of each current class. However I still get an "unchecked cast" warning.

// Old implementation for a specific type (SpecificType extends BaseType)
public class OneOldClass {

  public void MyMethod() {
    // ..
    SpecificType data = null;
    BaseType tmp = DAO.getData(String id, SpecificType.class);   // get data for specific type from hibernate
    if (tmp == null) {
      data = new SpecificType();
    }
    else {
      data = (SpecificType) tmp;
    }
    // update data..
  }

}

// My attempt at a generic version for the class
public abstract class MyBaseClass<T extends BaseType> {

  private Class<T> typeClass;   // is set in constructor!

  protected abstract T getNewType();   // return a new instance of the specific type

  public void myMethod() {
    // ..
    T data = null;
    BaseType tmp = DAO.getData(String id, typeClass);
    if (tmp == null) {
      data = getNewType();   // could use typeClass.newInstance(), but that needs extra exception handling
    }
    else {
      data = (T) tmp;   // <-- unchecked cast: 'BaseType' to 'T'
    }
    // update data..
  }

}

Is there a way to avoid the unchecked cast warning? Or is it safe to ignore it here? Or is there a better way to write this all?

[Rob Spoor]

    if (!typeClass.isInstance(tmp)) { // handles both null and other classes
      data = getNewType();   // could use typeClass.newInstance(), but that needs extra exception handling
    }
    else {
      data = typeClass.cast(tmp);
    }

That's actually kind of cheating since Class.cast uses the same unchecked cast, but at least it won't trouble you

[D. Ogranos]

Very nice, thank you!

[Rob Spoor]

You're welcome.