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Take a preliminary look at the complexity of OOP by examining some aspects of the System and PrintStream classes.

Revised: Mon Mar 28 11:44:44 CDT 2016

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This module takes a preliminary look at the complexity of OOP by examining some aspects of the System and PrintStream classes.

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This lesson introduces you to the use of the System and PrintStream classes in Java. This is our first introduction to the complexity that can accompany the OOP paradigm. It gets a little complicated, so you might need to pay special attention to the discussion.


What does the main method do?

The main method in the controlling class of a Java application controls the flow of the program.

The main method can also access other classes along with the variables and methods of those classes and of objects instantiated from thoseclasses.

The hello1 Application

Listing 1 shows a simple Java application named hello1 .

(By convention, class definitions should begin with an upper-case character. However, the original version of this module was written andpublished in 1997, before that convention was firmly established.)

Listing 1 . The program named hello1.
/*File hello1.java Copyright 1997, R.G.Baldwin **********************************************************/class hello1 { //define the controlling class //define main methodpublic static void main(String[] args){//display text string System.out.println("Hello World");}//end main }//End hello1 class. No semicolon at end of Java class.

Does this program Instantiate objects?

This is a simple example that does not instantiate objects of any other class.

Does this program access another class?

However, it does access another class. It accesses the System class that is provided with the Java development kit. (The System class will be discussed in more detail in a future module.)

The variable named out

The variable named out , referred to in Listing 1 as System.out , is a class variable of the System class. (A class variable is a variable that is declared to be static.)

Recall that a class variable can be accessed without a requirement to instantiate an object of the class. As is the case with all variables, the classvariable must be of some specific type.

Primitive variables vs. reference variables

A class variable may be a primitive variable , which contains a primitive value, or it may be a reference variable , which contains a reference to an object.

(I'll have more to say about the difference between primitive variables andreference variables in a future module.)

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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