Java downcast question

[Chad]

Given the following code...

class X {}
class Y extends X {}
class Z extends X {}

public class Main {

public static void main(String[] args) {
X x = new X();
Y y = new Y();
Z z = new Z();

Y o6 = (Y) x; //<--error
}

}

I get...

run:
Exception in thread "main" java.lang.ClassCastException: X cannot be
cast to Y
at Main.main(Main.java:12)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

Why can't I downcast X to Y? Y inherits X.

Chad