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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

super(3,x,4.5);

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

-end-

Questions & Answers

what are the important of economic to accounting students with references
salihu Reply
Economics is important because it helps people understand how a variety of factors work with and against each other to control how resources such as labor and capital get used, and how inflation, supply, demand, interest rates and other factors determine how much you pay for goods and services.
Muhammad
explain the steps taken by the government in developing rural market?
Azeem Reply
contribution of Adam smith in economics
abel Reply
I will join
Dexter
I will join
Patrick
Hey
Fatima
Hey
Amir
Hello
AS
hey
Umarou
I love this book and i need extra Economic book
Amir
Hey
Amir
what's happening here
AS
I love this book and i need extra Economic book
Amir
what is the meaning of function in economics
Effah Reply
Pls, I need more explanation on price Elasticity of Supply
Isaac Reply
Is the degree to the degree of responsiveness of a change in quantity supplied of goods to a change in price
Afran
Discuss the short-term and long-term balance positions of the firm in the monopoly market?
Rabindranath Reply
hey
Soumya
hi
Mitiku
how are you?
Mitiku
can you tell how can i economics honurs(BSC) in reputed college?
Soumya
through hard study and performing well than expected from you
Mitiku
what should i prepare for it?
Soumya
prepare first, in psychologically as well as potentially to sacrifice what's expected from you, when I say this I mean that you have to be ready, for every thing and to accept failure as a good and you need to change them to potential for achievement of ur goals
Mitiku
parna kya hai behencho?
Soumya
Hallo
Rabindranath
Hello, dear what's up?
Mitiku
cool
Momoh
good morning
Isaac
pls, is anyone here from Ghana?
Isaac
Hw s every one please
Afran
Ys please I'm in Ghana
Afran
Hello
OLANIYI
pls anyone from Nigeria
OLANIYI
am a new candidate here, can someone put me 2ru
OLANIYI
hello
OLANIYI
Pls economic A level exam tomorrow pls help me
akinwale
am from Ghana
Jacob
hi
Charles
Pls economic A level exam tomorrow pls help me
akinwale
Hi
Dev
bol Diya discuss ab krega v
Dev
hello Mr. Rabindranath
Dev
what do you want Dimlare
Dev
yes tell me your desire to have it
Dev
to have what?
OLANIYI
Good luck
JOSEPH
I want to know about economic A level tomorrow pls help
Lerato
okay
Umarou
okay
Umarou
what is firms
Anteyi Reply
A firm is a business entity which engages in the production of goods and aimed at making profit.
Avuwada
What is autarky in Economics.
Avuwada
what is choice
Tia Reply
So how is the perfect competition different from others
Rev Reply
what is choice
Tia
please what type of commodity is 1.Beaf 2.Suagr 3.Bread
Alfred Reply
1
Naziru
what is the difference between short run and long run?
Ukpen Reply
It just depends on how far you would like to run!!!🤣🤣🤣
Anna
meaning? You guys need not to be playing here; if you don't know a question, leave it for he that knows.
Ukpen
pls is question from which subject or which course
Ada
Is this not economics?
Ukpen
This place is meant to be for serious educational matters n not playing ground so pls let's make it a serious place.
Docky
Is there an economics expert here?
Docky
Okay and I was being serous
Anna
The short run is a period of time in which the quantity of at least one inputs is fixed...
Anna
that is the answer that I found online and in my text book
Anna
Elacisity
salihu
Meaning of economics
Suraj Reply
It will creates rooms for an effective demands.
Chinedum Reply
different between production and supply
babsnof
Hii
Suraj
hlo
eshita
What is the economic?
Suraj
Economics is a science which study human behavior as a relationship between ends and scarce means which has an alternative use.
Mr
what is supply
babsnof
what is different between demand and supply
Debless Reply
Demand refers to the quantity of products that consumers are willing to purchase at various prices per time while Supply has to do with the quantity of products suppliers are willing to supply at various prices per time. find the difference in between
Saye
Please what are the effects of rationing Effect of black market Effects of hoarding
Atty Reply
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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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