Extending Apex Classes

Please help me understand what is going on here. According to the documentation this code should work with no issues. I am trying to cast a return value of type parent class to a child class variable. This code compiles fine but throws

System.TypeException: Invalid conversion from runtime type Class1Test to Class1ExtensionTest

Here is the sample code

public virtual class Class1Test {

private string sCopy;
public Class1Test(string s){
sCopy = s;
}

public class Class1ExtensionTest extends Class1Test{

public Class1ExtensionTest(string s){
super(s);
}
}
}

public class TestClass{

public static testmethod void testmethod(){
Class1Test.Class1ExtensionTest t = (Class1Test.Class1ExtensionTest)testCasting();
}

private Class1Test testCasting( ){
return new Class1Test('This Should work');
}
}

July 20, 2009
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Superfell
You seem to have it back to front, your actual instance is an instance of the base class, you can't cast this to an instance of a sub-class, as it isn't a subclass.

July 20, 2009
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JoshVH
Doesn't the documentation say otherwise? It looks like they are casting a base object to a sub class object. Is it because it was first an instance of the sub class before it was put in a collection of type base class?

http://www.salesforce.com/us/developer/docs/apexcode/index_Left.htm#StartTopic=Content/apex_classes_casting.htm