JAVA
for Oracle Developers
Basic
Steps to write, compile, and run a JAVA application
Gathered By:
John Kazerooni
How
to install JAVA on my machine?
JAVA development
tool is free. If you don’t have it, you can download it now from the
“DownLoad JAVA”
link. Download the latest release to your desktop. Double click on the
downloaded icon on the desktop and follow the instructions. Use the default
folder, select components that you need (all), and define your default browser.
That is all! Don’t forget to view and read the README file. . (Make sure you
download the SDK, not the JRE.)
How
to write a JAVA application?
A JAVA application
is a standalone program.
Let us write a JAVA
application to display the “I will be a self learner!” message.
Step
#1: Write and Create a JAVA source file
Use the notepad
editor. Write, your first program,
IamSelfLeaner, to display the “I am self learner!” message as a JAVA
application program.
Then save your
application program as “c:\IamSelfLeaner.java” within the double quote and
exit from notepad. Be careful what you type. The JAVA compiler and interpreter
are very case-sensitive.
Notice
that the bold characters in the following listing are comments.
/******************************************************
*
The IamSelfLeaner class implements an application that
*
displays the "I am a self leaner!" message to the standard output.
******************************************************/
public class
IamSelfLearner {
public static void main(String[] args) {
// Display "I am a self learner!"
System.out.println("I am a self learner!");
}
}
A closer look at
your program:
The
Java language supports three kinds of comments:
/* text
*/ -- It
means the compiler ignores everything from /*
to */.
/** documentation
*/ -- Just like /* text */ and the
JDK javadoc uses it to generate documents.
// text
-- It
means that the compiler ignores everything from // to the end of the line.
A “class”
is a template that describes the object and its behavior. You create an object
by instantiating it to a class. Its data is stored in variables and its behavior
is implemented with methods. Think of a method like stored procedures in Oracle.
A
main is a method and it is the entry
point of every Java application. When you run an application with the Java
interpreter, you specify the name of the class that you want to run. The
interpreter invokes the main
method defined within that class. The main
method controls the flow of the program, allocates whatever resources are
needed, and runs any other methods that provide the functionality for the
application. If your application
does not have a main
method, the interpreter refuses to run it
and displays an error message. The
main
method may accept arguments
“public”
is the easiest access specifier. Any class, in any package, has access to a
class's public members. Declare public members only if such access can be seen
by outsiders.
The
following chart shows the access level permitted by each specifier.
Specifier
|
class
|
subclass
|
package
|
world
|
private
|
X
|
|
|
|
protected
|
X
|
X*
|
X
|
|
public
|
X
|
X
|
X
|
X
|
package
|
X
|
|
X
|
|
Variables
and Methods can be referred by join
the class name and the name of the class method or class variable together with
a period ("."). See System.out.println.
Step
#2: Compile your source program
Go to the MS-DOS or
Command prompt and change your current directory to the directory where you
saved the JAVA source program. Remember that the JAVA compiler be in your path.
If it is not, then set the path (set PATH=your java path/bin).
Example: MS-DOS>
c:\java folder\bin\javac IamSelfLearner.java
If there are no
errors, then you have successfully compiled your program. Now, you have
generated a JAVA bytecode file, IamSelfLearner.class. Now that you have the
class file (a JAVA bytecode file), you can run your program. This file can run
anywhere. That means that when you compile your program, you don't generate
instructions for one specific platform. They are instructions for the Java
Virtual Machine (Java VM).
Step
#3: Run the Program
In the same
directory, enter at the prompt type the following.
MS-DOS>java
IamSelfLearner
And now you should
see: I am a self learner!
If you got the “I
am a self learner” message then your program works. Congratulations!
If not, then make
sure that your are in the “class” folder or you might have to change your
CLASSPATH variable (set CLASSPATH=).
|