传递给超级构造函数的构造函数参数丢失

Question

In my GWT app I have a datatype (intended for building and tracking hierarchies of like objects) that extends a superclass, which in turn extends another, abstract superclass. There is a generic parameter declared in the abstract class which is then specified by each subclass as the type of itself. The structure is as follows:

public abstract class AbstractFoo<T extends AbstractFoo> {
     protected T parent;

     protected AbstractFoo(T parent){
          if (parent != null) parent.addChild(this);
          this.parent = parent;
     }
     //...
}

public class Foo<T extends Foo> extends AbstractFoo<T> {
     public Foo(T parent){
          super(parent);
          //...
     }
}

public class SpecialFoo<T extends SpecialFoo> extends Foo<T> {
     public SpecialFoo(T parent){
          super(parent);
          //...
     }
}

When I pass a parent argument to the constructor of SpecialFoo, the constructor of Foo will be called as a superconstructor, and that constructor will in turn call the constructor of AbstractFoo as a superconstructor.

The problem I have is that the parent argument gets reset to NULL when passed from Foo to AbstractFoo. I have no idea why this happens. Can anyone tell me what I need to do in order to pass it through to the abstract base class unharmed?

---

EDIT: I think I've solved it... The trick seems to be that I have to declare the parent argument in each subclass, so that there is a more specific reference to it, like so:

 public abstract class AbstractFoo<T extends AbstractFoo> {
      protected T parent;

      protected AbstractFoo(T parent){
           if (parent != null) parent.addChild(this);
           this.parent = parent;
      }
      //...
 }

 public class Foo<T extends Foo> extends AbstractFoo<T> {
      protected T parent;

      public Foo(T parent){
           super(parent);
           //...
      }
 }

 public class SpecialFoo<T extends SpecialFoo> extends Foo<T> {
      private SpecialFoo parent;

      public SpecialFoo(T parent){
           super(parent);
           //...
      }
 }

Answer 1

Review these points:

1. Prove POSITIVELY that you are receiving a null argument in the constructor (print it);
2. Check for other constructors in your classes. You may be calling a constructor you are not expecting to call, especially due to the generic type of that argument.

Answer 2

您是否检查过您的父母是否为非 null给了SpecialFoo构造函数？