问不能将类转换为子类吗？

EN

class Mid1Prob1 {
    public static void main(String[] args) {
        System.out.println("Testing...");
        int x = 3;
        System.out.println(3);
        System.out.println((int) x); // legal to cast primitive value to the same type as itself
        System.out.println((long) x); // legal to cast primitive value to a super type
        System.out.println((short) x); // legal to cast a primitive value to a sub type, but may lose information

        Actual act = new Actual();
        System.out.println(((Actual) act) .x); // legal to cast a reference value to the same class as itself
        System.out.println(((Super) act) .x); // legal to cast a reference value to a superclass of itself, as long as the superclass is actually a superclass of the current class
        System.out.println(((Sub) act) .x); // run-time error, cannot cast a reference value to its subclass
    }
}

class Super {
    public int x = 999;
}

class Actual extends Super {
    public int x = 666; // variables can be public in package-private class
}

class Sub extends Actual {
    public int x = 333;
}