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Earlier modules have touched briefly on the topic of variables. This module discusses Java variables in depth.

Revised: Mon Mar 28 12:30:19 CDT 2016

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Earlier modules have touched briefly on the topic of variables. This module discusses Java variables in depth.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand Listings while you are reading about them.


  • Figure 1 . Screen output from the program named simple1.
  • Figure 2 . Information about the primitive types in Java.
  • Figure 3 . Rules for naming variables.
  • Figure 4 . Rules for legal identifiers.
  • Figure 5 . Scope categories.


  • Listing 1 . Source code for the program named simple1.
  • Listing 2 . Declaring and initializing two variables named ch1 and ch2.
  • Listing 3 . Display the character.
  • Listing 4 . Beginning of a while loop.
  • Listing 5 . Beginning of the main method.
  • Listing 6 . The program named wrapper1.
  • Listing 7 . Aspects of using a wrapper class.
  • Listing 8 . The program named member1.
  • Listing 9 . Initialization of variables.


The first step

The first step in learning to use a new programming language is usually to learn the foundation concepts such as

  • variables
  • types
  • expressions
  • flow-of-control, etc.

This and several future modules concentrate on that foundation.

A sample program

The module begins with a sample Java program named simple1 . The user is asked to enter some text and to terminate with the # character.

(This program contains a lot of code that you are not yet prepared to understand. For the time being, just concentrate on the use of variables in theprogram. You will learn about the other aspects of the program in future modules.)

The program loops, saving individual characters until encountering the # character. When itencounters the # character, it terminates and displays the character entered immediately prior to the # character.

Sample program named simple1

A complete listing of the program named simple1 is provided in Listing 1 . Discussions of selected portions of theprogram are presented later in the module.

Listing 1 . Source code for the program named simple1.
/*File simple1.java Copyright 1997, R.G.Baldwin This Java application reads bytes from the keyboard untilencountering the integer representation of '#'. At the end of each iteration, it saves the byte received andgoes back to get the next byte. When the '#' is entered, the program terminates input anddisplays the character which was entered before the #. **********************************************************/class simple1 { //define the controlling class //It is necessary to declare that this method// can throw the exception shown below (or catch it). public static void main(String[]args) //define main throws java.io.IOException {//It is necessary to initialize ch2 to avoid a compiler // error (possibly uninitialized variable) at the// statement which displays ch2. int ch1, ch2 = '0';System.out.println( "Enter some text, terminate with #");//Get and save individual bytes while( (ch1 = System.in.read() ) != '#')ch2 = ch1; //Display the character immediately before the #System.out.println( "The char before the # was " + (char)ch2);}//end main }//End simple1 class.

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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