Core Java tutorials.
In Java object typecasting, type cast of 1 object reference is possible to another object reference. Suck type of casting is done with superclass, subclass or class types. Compile time rules or runtime rules are present in Java for casting.
Class relationship is the basic thing at which Object reference is dependent. Any object reference could be assigned to reference variable of type object because the object class is usually the superclass, for each Java class.