Java...how does it all start?

[Mike Skvarenina]

OK, so I am an experienced computer programmer in VB and RPG getting ready
to make the leap to Java! But to this day I don't see the big picture.
Do I make .exe's with Java or do all my programs run out of a browser. If
I always run out of a browser, I guess the database resides on the same machine
as the web server?

I guess I am looking for a graphical overview of how Jva intergrates with
the computer world...or at least a good explaination. Can anyone shed some
light here?

[Kent]

Hi,

I think I can explain most of what you're asking. Java is, in theory, platform
independent. That is, a compiled Java class can be executed on any Java-supporting
system.

When a .java file is compiled, it is compiled into Java Byte Codes (stored
in .class files). These class files are executed using the Java Virtual Machine
(JVM). The JVM is the platform-dependent software.

To execute a Java class you will need a JVM on your machine. The JVM converts
the byte codes into machine code specific to your machine. So, in effect,
there is an extra layer between the 'executable'.

Java can be used on the server (eg. a Java class to interact with a database
that also resides on the server) or on the client (an Applet for example).
Java is not limited to web purposes. For example, I could write a Java program
to encrypt/decrypt a PIN for a project I'm working on. I can compile and
run this Java program via the command line using 'javac' (java compiler)
and 'java' respectively.

For a database to be useful from a web point of view, it really needs to
reside on the server. You can't expect each user to download the database,
plonk it on their machine, do their thing, then upload the database again!

Having the database on the server allows all users to use the same data at
effectively the same time. Using JSP (Java Server Pages) you can invoke methods
on Java classes (sitting on the server) to do database interactions (save
records, return records etc.).

I hope this explains a bit...

Kent


"Mike Skvarenina" <mskvarenina@usa.net> wrote:
>
>OK, so I am an experienced computer programmer in VB and RPG getting ready
>to make the leap to Java! But to this day I don't see the big picture.

>Do I make .exe's with Java or do all my programs run out of a browser.
If
>I always run out of a browser, I guess the database resides on the same
machine
>as the web server?
>
>I guess I am looking for a graphical overview of how Jva intergrates with
>the computer world...or at least a good explaination. Can anyone shed some
>light here?
>