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What does this allow you to do?

When a reference to an object is held by a reference variable whose type matches an interface implemented by the class from which the object wasinstantiated, that reference can be used to call any method declared in or inherited into that interface.

(That reference cannot be used to call methods not declared in or not inherited into that interface.)

In this simple case ...

The method named intfcMethod is declared in the interface named X and implemented in the class named A .

Therefore, the method named intfcMethod can be called on an object instantiated from the class named A when the reference to the object is held in a reference variable of the interface type.

(The method could also be called if the reference is being held in a reference variable of declared type A .)

The call to the method named intfcMethod causes the text A-intfcMethod to appear on the screen.

Back to Question 4

Answer 3

C. Base A-intfcMethod

Explanation 3

What is runtime polymorphic behavior?

One way to describe runtime polymorphic behavior is:

The runtime system selects among two or more methods having the same signature, not on the basis of the type of the reference variable in which an object'sreference is stored, but rather on the basis of the class from which the object was originally instantiated.

Illustrates simple class and interface inheritance

The program defines a class named Base , and a class named A , which extends Base , and implements the interface named X , as shown in the following fragment.

class Base{ public void inherMethod(){System.out.print("Base "); }//end inherMethod()}//end class Base class A extends Base implements X{public void inherMethod(){ System.out.print(" A-inherMethod "); }//end inherMethod()public void intfcMethod(){System.out.print("A-intfcMethod "); }//end intfcMethod()}//end class A interface X{public void intfcMethod(); }//end X

Define an interface method

The interface named X declares a method named intfcMethod . A concrete definition of that method is defined in the class named A .

A new object of type Base

The code in the following fragment instantiates a new object of the class Base and calls its inherMethod . This causes the word Base to appear on the output screen. There is nothing special about this. This is a simple example of the use of an object's reference to call one of itsinstance methods.

void doIt(){ Base myVar1 = new Base();myVar1.inherMethod();

A new object of type A

The following fragment instantiates a new object of the class A and calls its intfcMethod . This causes the text A-intfcMethod to appear on the output screen. There is also nothing special about this. This is also a simple example of the use of anobject's reference to call one of its instance methods.

A myVar2 = new A(); myVar2.intfcMethod();System.out.println(""); }//end doIt()

Not polymorphic behavior

The fact that the class named A implements the interface named X does not indicate polymorphic behavior in this case. Rather, this program is an example of simple class and interface inheritance.

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
right! what he said ⤴⤴⤴
greetings from Iran
salut. from Algeria
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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