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public static final double PI

The double value that is closer than any other to pi, the ratio of the circumference of a circle to its diameter.

The constant named PI

You may recognize the constant named PI from your high school geometry class.

Whenever you need the value for the constant PI , you shouldn't have to instantiate an object just to get access to it. Furthermore, your class shouldnot be required to have any special package relationship with the Math class just to get access to PI .

The good news ...

Because PI is declared to be both public and static in the Math class, it is readily available to any code in any method in any Java program that has access to the standard Java class library.

How is PI accessed?

PI can be accessed by using an expression as simple as that shown below, which consists simply of the name of the class and the name ofthe variable joined by a period (Math.PI) .

double piRSquare = Math.PI * R * R;

No notion of public local variables

As a result of the above, many of you may have become accustomed to associating the keyword public with the keyword final . However, if you missed this question and you have read the explanation to thispoint, you must also remember that there is no notion of public or private for local variables. Therefore, when this program was compiled under JDK 1.3, a compiler error was produced. That compiler error is partiallyreproduced below:

Ap103.java:16: illegal start of expressionpublic final int x = 5;

Back to Question 4

Answer 3

A. Compiler Error

Explanation 3

The final keyword

The final keyword can be applied in a variety of ways in Java. This includes:

  • final parameters
  • final methods
  • final classes
  • final variables (constants)

Behaves like a constant

When the final keyword is applied to a variable in Java, that causes the variable to behave like a constant. In other words, the value of the variablemust be initialized when it is declared, and it cannot be changed thereafter (see the exception discussed below) .

Apply to local or member variables

The final keyword can be applied to either local variables or member variables. (In case you have forgotten, local variables are declared inside a method or constructor, while member variables are declared inside a class, but outside amethod.)

So, what is the problem?

The problem with this program is straightforward. As shown in the following code fragment, after declaring a final local variable and initializing its value to 5, the program attempts to change the value stored in that variable to 10.This is not allowed.

final int x = 5; x = 10;

A compiler error

JDK 1.3 produces the following error message:

Ap102.java:17: cannot assign a value to finalvariable x x = 10;

An interesting twist - blank finals

An interesting twist of the use of the final keyword with local variables is discussed below.

Background information

Regardless of whether or not the local variable is declared final , the compiler will not allow you to access the value in a local variable if thatvariable doesn't contain a value. This means that you must always either initialize a local variable or assign a value to it before you can access it.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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
How can I make nanorobot?
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
how can I make nanorobot?
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
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