Question regarding Polymorphism.

[Thomas Markl]

Please consider the code as follows:
The result is „Child.test“ as first line because anSub is of Base reference type
But of Child object type. When an instance method is overridden then the
object type counts if the method is called. Therefore Child.test() method
is called and printed. This behavour is called Polymorphism.
But then ssubObj is fully a a Base oject with „Base ssubObj = (Base)ansub.
So why is Child.test() still called, shouldn’t it be Base.test()?

class Base {
  void test() { 
    System.out.println("Base.test()");
  }
}
class Child extends Base {
// THIS HIDES THE BASE CLASS METHOD
  void test() {                    
    System.out.println("Child.test()");
  }
}
public class OverrideStaticTest1c {
  static public void main(String[] a) {
    Base anSub = new Child();
    anSub.test();  //prints Child.test() which is ok.
    Base ssubObj = (Base)anSub;
// creates from Child objecttype anSub an real Base object
// Why does ssubOjj.test print out "Child.test() instead of "Base.test()"?
    ssubObj.test();//prints Child.test(), why not Base.test()? 
  } 
}

[Ilja Preuss]

Casting doesn't affect the type of an object at all, only the type of a reference!

[NI Java Music]

I think the problem you have identified is solved by understanding object referencing. (By the way I am probably more of a beginner than you so please feel free to have me contradicted!). You have created an object called anSub. But in the line:
Base ssubObj = (Base)anSub;
it seems to me that ssubObj is a reference to an object called asSub. So if you forget about casting for a moment, and assume you have one object called anSub with a reference ssubObj pointing to it, then its like having two of the exact same thing(but there is only one object). However you have casted the anSub to a class type (the superclass Base). It changes the type, but it doesn't change what is in the object that ssubObj points to namely your Child print statement.
As I say, I see it this way, but I am far from an expert. Please don't rely on what I am saying, but let me know if you agree or not.

[Jessica Sant]

"NI Java Music"-
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[Ilja Preuss]

Originally posted by NI Java Music:
I think the problem you have identified is solved by understanding object referencing. (By the way I am probably more of a beginner than you so please feel free to have me contradicted!). You have created an object called anSub. But in the line:
Base ssubObj = (Base)anSub;
it seems to me that ssubObj is a reference to an object called asSub. So if you forget about casting for a moment, and assume you have one object called anSub with a reference ssubObj pointing to it, then its like having two of the exact same thing(but there is only one object). However you have casted the anSub to a class type (the superclass Base). It changes the type, but it doesn't change what is in the object that ssubObj points to namely your Child print statement.
As I say, I see it this way, but I am far from an expert. Please don't rely on what I am saying, but let me know if you agree or not.

You are nearly correct - in fact, even anSub is the name of a *reference*, the actual object it is pointing to doesn't have a name at all!