Question on Object Orientation Topic

public class Redwood extends Tree {
4. public static void main(String[] args) {
5. new Redwood().go();
6. }
7. void go() {
8. go2(new Tree(), new Redwood());
9. go2((Redwood) new Tree(), new Redwood());
10. }
11. void go2(Tree t1, Redwood r1) {
12. Redwood r2 = (Redwood)t1;
13. Tree t2 = (Tree)r1;
14. }
15. }
16. class Tree { }


Question: Why would this ended up with only exception being thrown?
go2(new Tree(), new Redwood()); -- allowed in Java?
(sorry i'm quite weak on this)
Thanks in advanced.

The go method takes a Tree and a Redwood.
The

Code:

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go2((Redwood) new Tree(), new Redwood());

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call is allowed by the compiler because a Redwood is a Tree. That's all the compiler can do for you.
At runtime, the JVM is being asked to change a Tree that is not a Redwood to a Redwood so it doesn't like that.