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The compiler does not see any Update method in the Object object.
You can use casting to tell the compiler what class is contained in the Object object.
((SomeClass)theObject).theMethod(); //...

Each variable is declared as one data type. For classes, since all classes extend the Object class, then a variable declared as an Object can be assigned a reference to any class. Primitive...

Are you talking about when one class extends another?
For example if ClassB extends ClassA
then a variable declared to hold a reference to a ClassA object can contain a reference to a ClassB...