Question

Why am I not able to reference object of “Object” class typecasted and referenced to Some class’s object. Following code explains it. It is hard to put in words. Meaning, object of Super class Object should be able to reference any type of Class’s object.

public class ChildClass {

public static void main(String[]args){
    Simple obj1=new Simple();
    Object obj2=(Simple)obj1;
    System.out.println("1-obj1.a is "+ obj1.a+" obj1.name is "+obj1.name);
    System.out.println("2-obj2.a is "+ obj2.a+" obj2.name is "+obj2.name);/*a cannot be resolved or is not a 
    field*/
    doSomething(obj2);
    System.out.println("3-obj2.a is "+ obj2.a+" obj2.name is "+obj2.name);/*a cannot be resolved or is not a 
    field*/
    System.out.println("4-obj1.a is "+ obj1.a+" obj1.name is "+obj1.name);
}

private static void doSomething(Object obj2) {
    obj2.a=99;//a cannot be resolved or is not a field
    obj2.name="new name";//name cannot be resolved or is not a field

}
class Simple {

    int a=9;
    String name="something";

}

}

Answer 1

You need to cast the Object to Simple if you really want the argument to be of type Object:

private static void doSomething(Object obj2) {
    ((Simple)obj2).a = 99;
    ((Simple)obj2).name = "new name";
}

or, to make it a little more safe:

private static void doSomething(Object obj2) {
    if (obj2 instanceof Simple) {
        Simple simple = (Simple) obj2;  
        simple.a = 99;
        simple.name = "new name";
    }
}

You seem to have it backwards. A reference of type Simple can be used to call methods of Object, but not the other way around.