Java 5.0 Generics

Question

Hi Guys ,
Been playing around with Generics and have been confused with them.
I have a generic CRUDAction :
public abstract class CRUDAction<T, U, F> extends PageBean implements Preparable {
protected U primaryKey;
     * @return the primaryKey
     public U getPrimaryKey() {
          return this.primaryKey;
     * @param primaryKey the primaryKey to set
     public void setPrimaryKey(U primaryKey) {
          this.primaryKey = primaryKey;
I'm using Struts2 and when the param interceptor runs it sets primaryKey with the submitted value.
Everyting is fine So far.
I create a new action based on this abstract with real types :
public class UserAction extends CRUDAction<User,Integer,UserFilter> {}
What I thought would happen was that setPrimaryKey(U primaryKey) --> setPrimaryKey(Integer primaryKey) ..
but I don't know why when I debug, struts2 is able to set String object through the setPrimaryKey method.
Am I doing something wrong ?

Answer 1

Seems like Struts 2 don't support generics (I never used struts).
In class file, method setPrimaryKey in UserAction have signature setPrimaryKey(Object), but not setPrimaryKey(Integer) This method is inherited from parent, where its argument is "erased" to Object during compilation. Information about actual type arguments (that argument for setPrimaryKey should be Integer) is avaliable via reflection, but application or library (struts2) should be aware of it.