Parent..child clas type casting???

Question

Hi All,
I have a query, please have a look:
I have a parent class :: parent (getting compiled well , it's a simple class only)
I have a child class :: child
please see the code for child class below:
public class child extends parent
   public static void main(String args[])
      //child c = new mainClass();   //STATEMENT1. This gives comiplation error for incompatible types.
      child c = (child) new mainClass(); //STATEMENT2. this statement works fine
}Is there any reason why typecasting does not occur in statement 1 where as it is working fine in statement 2?
I am intending to do the same thing in both statement 1 and 2.
Any specific reason why implicit type casting does not work?
Please comment.
TIA
Ayusman

Answer 1

If mainclass is not a subclass of child, then you can't assign it as in #1.
#2 will work at compile time if the compiler cannot be sure that a reference to a mainclas is cannot be a reference to a child.
If #1 fails and #2 compiles, than I can only assume that child extends mainClass. In both cases, all the compiler knows about the new is that is returns a reference to a mainClass.
#1 is allowed only if all mainClasses are childs--that is, if mainClass extends child.
#2 is allowed at compile time if and only if a reference to a mainClass could be a reference to child. In this case that would have to mean that child extends mainClass. The compiler doesn't know that you're pointing at an object that is only a mainClass. All it knows is that it's a mainClass or one of it's subclasses. However, since it is in fact only a mainClass and not a child, you will get a ClassCastException at runtime.