ClassCastException will be thrown when the code attempts to downcast a Tree to a Redwood

In below code, at Line 7 when we are downcasting Tree to Redwood there is no error, but why we get a runtime error at line 10 when downcasting Tree to Redwood

public class Redwood extends Tree {
    public static void main(String[] args) {
        new Redwood().go();
    }
    void go() {
        go2(new Tree(), new Redwood());
        go2((Redwood) new Tree(), new Redwood());// no error here
    }
    void go2(Tree t1, Redwood r1) {
        Redwood r2 = (Redwood)t1;// runtime error here
        Tree t2 = (Tree)r1;
    }
}
class Tree { }

Well, while a Redwood instance is always a Tree instance, not all Tree instances are a Redwood. When you create a Tree instance (with new Tree()) it is certainly not a Redwood instance, and cannot be cast to Redwood.

Redwood r2 = (Redwood)t1; throws a ClassCastException when t1 is not a Redwood. In the first call to go2, the first argument is new Tree(), which is not a Redwood.

Oh, and the reason you see an error here - Redwood r2 = (Redwood)t1; (line 10) and not on line 7 (go2((Redwood) new Tree(), new Redwood());) is that line 10 is executed first, at the first call to go2() (line 6). If you comment line 6, you'll get an exception in line 7.