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Not runtime polymorphic behavior

Just for the record, the above invocation of the method does not constitute runtime polymorphism (in my opinion) . I included that invocation of the method to serve as a backdrop for what follows.

If this is runtime polymorphism, it is not a very significant example, because there was no requirement for the runtime system to decide betweendifferent methods having the same name. The runtime system simply executed a method belonging to an object using a reference of the same type as the object.

This is runtime polymorphic behavior

However, the call to the method in Listing 4 does constitute runtime polymorphism.

Listing 4 . This is runtime polymorphic behavior.

//Following will also compile // and run due to polymorphic// behavior. ((A)var).m();

The statement in Listing 4 casts the reference down to type A and calls the method named m on that reference.

The method output

Here is the punch line. Not only does the statement in Listing 4 compile and run successfully, it produces the following output, (which is exactly the same output as before) :

m in class B

The same method was executed in both cases

Very important

It is very important to note that this output, (produced by casting the reference variable to type A instead of type B ) , is exactly the same as that produced by the earlier call to the method when thereference was cast to type B . This means that the same version of the method was executed in both cases.

This confirms that even though the type of the reference was converted to type A , (rather than type Object or type B ) , the overridden version of the method defined in class B was actually executed.

This is runtime polymorphic behavior in a nutshell.

The version of the method that was executed was based on the actual type of the object, B , and not on the type of the reference, A . This is an extremely powerful and useful concept.

Another invocation of the method

Now take a look at the statement in Listing 5 . Will this statement compile and execute successfully? If so, which version of the method will be executed?

Listing 5 . A failed attempt.

//Following will not compile //var.m();

(That was easy. The answer to the question is given in Listing 5 ) .

Compiler error

The code in Listing 5 attempts, unsuccessfully, to call the method named m using the reference variable named var , which is of type Object . The result is a compiler error, which reads something like the following:

error CS0117: 'object' does not contain a definition for 'm'

Some important rules

The Object class does not define a method named m . Therefore, the overridden method named m in the class named B is not an overridden version of a method that is defined in the class named Object .

Necessary, but not sufficient

Runtime polymorphism based on class inheritance requires that the type of the reference variable be a superclass of the class from which the object (on which the method will be called) is instantiated.

At least this requirement is true if a significant decision among methods is to be made.

Questions & Answers

what is math number
Tric Reply
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
Need help solving this problem (2/7)^-2
Simone Reply
what is the coefficient of -4×
Mehri Reply
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
I'm 13 and I understand it great
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
is it a question of log
I rally confuse this number And equations too I need exactly help
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Commplementary angles
Idrissa Reply
im all ears I need to learn
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greetings from Iran
salut. from Algeria
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Source:  OpenStax, Xna game studio. OpenStax CNX. Feb 28, 2014 Download for free at https://legacy.cnx.org/content/col11634/1.6
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