Inheritance questions

Question

Say a superclass has 3 methods and 3 properties. NExt, I create a subclass which overrides these same 3 methods and properties. Either way, my question really is this... When casting up and down, when it is a subclass and a super class reference, are the properties preserved when it is cast(implicitly) up to a superclass reference, so that, in case it needs to be cast back down (explicitly) to its original subclass form, the subclass properties can still be referred to? Are the original variables still preserved (much like a static variable)?

Answer 1

are the properties preserved when it is cast(implicitly) up to
a superclass reference, so that, in case it needs to be cast backAn object instance does not change when it's casted into a superclass reference. This means it can be casted back (if this weren't the case, then all methods that return Object would be pretty useless).
In addition, accessing an object method via a superclass reference does not mean that you'll invoke a superclass method. Instead, it invokes the method appropriate to the object (otherwise overriding and polymorphism would be pretty useless).
However, accessing an object's instance variable via a superclass reference does access the superclass variable, not the subclass variable.
I would suggest playing with this for a while ... here's something to start with:
public class DROCPDP
    public static void main( String argv[] )
    throws Exception
        Base a = new Base();
        Sub b = new Sub();
        Base c = (Base)b;
        Sub d = (Sub)c;
        System.out.println("\nOperations on A:");
        System.out.println("a.var = " + a.var);
        a.method();
        System.out.println("\nOperations on B:");
        System.out.println("b.var = " + b.var);
        b.method();
        System.out.println("\nOperations on C:");
        System.out.println("c.var = " + c.var);
        c.method();
        System.out.println("\nOperations on D:");
        System.out.println("d.var = " + d.var);
        d.method();       
    private static class Base
        public String var = "Base";
        public void method()
            System.out.println("Called Base.method; variable = " + var);
    private static class Sub extends Base
        public String var = "Sub";
        public void method()
            System.out.println("Called Sub.method; variable = " + var);
}