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The rules for legal identifiers are shown in Figure 4 .

Figure 4 . Rules for legal identifiers.
  • In Java, a legal identifier is a sequence of Unicode letters and digits of unlimited length.
  • The first character must be a letter.
  • All subsequent characters must be letters or numerals from any alphabet that Unicode supports.
  • In addition, the underscore character (_) and the dollar sign ($) are considered letters and may be used as any character including the firstone.

Scope

What is the scope of a Java variable?

The scope of a Java variable is defined by the block of code within which the variable is accessible.

(Briefly, a block of code consists of none, one, or more statements enclosed by a pair of matching curly brackets.)

The scope also determines when the variable is created (memory set aside to contain the data stored in the variable) and when it possibly becomes a candidate for destruction (memory returned to the operating system for recycling and re-use) .

Scope categories

The scope of a variable places it in one of the four categories shown in Figure 5 .

Figure 5 . Scope categories.
  • member variable
  • local variable
  • method parameter
  • exception handler parameter

Member variable

A member variable is a member of a class (class variable) or a member of an object instantiated from that class (instance variable) . It must be declared within a class, but not within the body of a method or constructor ofthe class.

Local variable

A local variable is a variable declared within the body of a method or constructor or within a block of code contained within the body of a method orconstructor.

Method parameters

Method parameters are the formal arguments of a method. Method parameters are used to pass values into and out of methods. The scope of a method parameter isthe entire method for which it is a parameter.

Exception handler parameters

Exception handler parameters are arguments to exception handlers. Exception handlers will be discussed in a future module.

Illustrating different types of variables in Java

The Java program shown in Listing 8 illustrates

  • member variables (class and instance) ,
  • local variables, and
  • method parameters.

An illustration of exception handler parameters will be deferred until exception handlers are discussed in a future module.

Listing 8 . The program named member1.
/*File member1.java Copyright 1997, R.G.Baldwin Illustrates class variables, instancevariables, local variables, and method parameters. Output from this program is:Class variable is 5 Instance variable is 6Method parameter is 7 Local variable is 8**********************************************************/ class member1 { //define the controlling class//declare and initialize class variable static int classVariable = 5;//declare and initialize instance variable int instanceVariable = 6;public static void main(String[] args){ //main methodSystem.out.println("Class variable is " + classVariable);//Instantiate an object of the class to allow for // access to instance variable and method.member1 obj = new member1(); System.out.println("Instance variable is "+ obj.instanceVariable); obj.myMethod(7); //call the method//declare and intitialize a local variable int localVariable = 8;System.out.println("Local variable is " + localVariable);}//end main void myMethod(int methodParameter){System.out.println("Method parameter is " + methodParameter);}//end myMethod }//End member1 class.

Declaration of local variables

In Java, local variables are declared within the body of a method or within a block of code contained within the body of a method.

Scope of local variables

The scope of a local variable extends from the point at which it is declared to the end of the block of code in which it is declared.

What is a "block" of code?

A block of code is defined by enclosing it within curly brackets as in { ... }.

Therefore, the scope of a local variable can be the entire method, or can reduced by declaring it within a block of code within the method.

Special case, scope within a for loop

Java treats the scope of a variable declared within the initialization clause of a for statement to be limited to the total extent of the for statement.

A future module will explain what is meant by a for statement or a for loop.

Initialization of variables

Initializing primitive local variables

Local variables of primitive types can be initialized when they are declared using statements such the one shown in Listing 9 .

Listing 9 . Initialization of variables.
int MyVar, UrVar = 6, HisVar;

Initializing member variables

Member variables can also be initialized when they are declared.

In both cases, the type of the value used to initialize the variable must match the type of the variable.

Initializing method parameters and exception handler parameters

Method parameters and exception handler parameters are initialized by the values passed to the method or exception handler by the calling program.

Run the programs

I encourage you to copy the code from Listing 1 , Listing 6 , and Listing 8 . Compile the code and execute it. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

Miscellaneous

This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Jb0200: Java OOP: Variables
  • File: Jb0200.htm
  • Originally published: 1997
  • Published at cnx.org: 11/18/12
Disclaimers:

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

-end-

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
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
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
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salma
Commplementary angles
Idrissa Reply
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Sherica
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Sherica
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Tamia
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Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
how do you translate this in Algebraic Expressions
linda Reply
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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