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Figure 2 . Text output for overridden ToString method and class B.
ToString in class B You should recognize this as the text that was encapsulated in the String object returned by the overridden version of the ToString method defined in the class named B . (See Listing 2 .)
This verifies that even though the reference to the object of the class B was stored in a reference variable of type Object , the overridden version of the ToString method in the class named B was executed (instead of the default version defined in the class named Object) . This is runtime polymorphic behavior , as described in a previous module.
The selection of a method for execution is based on the actual type of object whose reference is stored in a reference variable, and not on the type of the reference variable on which the method is called.
Finally, the code in Listing 6
Listing 6 . An object of the class C.
Object varC = new C();
String v3 = varC.ToString();Console.WriteLine(v3);
//Pause until user presses any key.Console.ReadKey();}//end Main
}//end class Polymorph04 By now, you should know what to expect in the way of text appearing on the computer screen. The code in Listing 6 causes the text shown in Figure 3 to be displayed.
Figure 3 . Text output for overridden ToString method and class C.
ToString in class C This confirms what you should already have known by now. In particular, even though the reference to the object of the class C was stored in a reference variable of type Object , the overridden version of the ToString method defined in the class named C was executed. Again, this is runtime polymorphic behavior based on class inheritance and method overriding.
It is also very important to note that no downcasting was required in order to call the ToString method in any of the cases shown above.
Because a default version of the ToString method is defined in the Object class, that method can be called without a requirement for downcasting on a reference to any object stored in a variable oftype Object . This holds true for any of the methods defined in the class named Object .
Therefore, if we create an array object designed to store references of type Object , we can store (potentially mixed) references to any type of object in that array. We can later call any of the methods definedin the Object class on any of the references stored in the array.
The result will be the execution of the overridden version of the method as defined in the class from which the object was instantiated, or the versioninherited into that class if the method is not overridden in that class. Current jargon would say that the behavior of the method is appropriate for the type of object on which it is called.
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