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So, what is the twist?

Unlike final member variables of a class, the Java compiler and runtime system do not require you to initialize a final local variable when you declare it. Rather, you can wait and assign a value to it later. (Some authors refer to this as a blank final.) However, once you have assigned a value to a final local variable, you cannot change that value later.

The bottom line

Whether you initialize the final local variable when you declare it, or assign a value to it later, the result is the same. It behaves as a constant.The difference is that if you don't initialize it when you declare it, you cannot access it until after you assign a value to it.

Back to Question 3

Answer 2

F. 20, 10

Explanation 2

Calling a parameterized constructor

This is a relatively straightforward implementation of the use of the super keyword in a subclass constructor to call a parameterized constructor in the superclass.

The interesting code in the program is highlighted in the following fragment. Note that quite a lot of code was deleted from the fragment for brevity.

class Superclass{ //...public Superclass(int x){//... }//end constructor//...}//end Superclass class Subclass extends Superclass{//...public Subclass(){ super(20);//... }//end constructor//...}//end Subclass

Using the super keyword

The code that is of interest is the use of super(20) as the first executable statement in the Subclass constructor to call the parameterized constructor in the superclass, passing a value of 20 as aparameter to the parameterized constructor.

Note that when the super keyword is used in this fashion in a constructor, it must be the first executable statement in the constructor.

As before, the program plays around a little with initial values for instance variables to see if you are alert, but the code that is really of interest ishighlighted in the above fragment.

Back to Question 2

Answer 1

D. 5, 10

Explanation 1

The execution of constructors

The purpose of this question and the associated answer is to illustrate explicitly what happens automatically by default regarding the execution ofconstructors.

The Subclass constructor

This program defines a class named Subclass , which extends a class named Superclass . A portion of the Subclass definition, including its noarg constructor is shown in the following code fragment. (The class also defines a getter method, which was omitted here for brevity.)

class Subclass extends Superclass{ private int y = 2;public Subclass(){super(); y = 10;}//end constructor//... }//end Subclass

The super keyword

The important thing to note in the above fragment is the statement containing the keyword super .

The super keyword has several uses in Java. As you might guess from the word, all of those uses have something to do with the superclassof the class in which the keyword is used.

Invoke the superclass constructor

When the super keyword (followed by a pair of matching parentheses) appears as the first executable statement in a constructor, this is an instruction tothe runtime system to first call the constructor for the superclass, and then come back and finish executing the code in the constructor for the class towhich the constructor belongs.

Call the noarg superclass constructor

If the parentheses following the super keyword are empty, this is an instruction to call the noarg constructor for the superclass.

Invoke a parameterized superclass constructor

If the parentheses are not empty, this is an instruction to find and call a parameterized constructor in the superclass whose formal arguments match the parameters in the parentheses.

Invoke the noarg superclass constructor by default

Here is an important point that is not illustrated above. If the first executable statement in your constructor is not an instruction to call the constructor for the superclass, an instruction to call the noarg constructor for the superclass will effectively be inserted into yourconstructor code before it is compiled.

Therefore, a constructor for the superclass is always called before the code in the constructor for your new class is executed.

You can choose the superclass constructor

The superclass constructor that is called may be the noarg constructor for the superclass, or you can force it to be a parameterizedconstructor by inserting something like


as the first instruction in your constructor definition.

Always have a noarg constructor ...

Now you should understand why I told you in an earlier module that the classes you define should almost always have a noarg constructor, either the default noarg version, or a noarg version of your own design.

If your classes don't have a noarg constructor, then anyone who extends your classes will be required to put code in the constructor for theirnew class to call a parameterized constructor in your class.

In this program, the super(); statement in the Subclass constructor causes the noarg constructor for the Superclass to be called. That noarg constructor is shown in the following code fragment.

class Superclass{ private int x = 1;public Superclass(){x = 5; }//end constructor//...}//end Superclass

Additional code

Beyond an exposure and explanation of the use of the super keyword to call the superclass constructor, this program plays a few games with initial valuesof instance variables just to see if you are alert to that sort of thing. However, none of that should be new to you, so I won't discuss it further here.

Back to Question 1


Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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