NOTE: Please i do not expect everybody to read this on-line, you can copy the pages to a storage device
and take time to go through it or you can also print it out.

Welcome to this thread. Having seen some threads in this forum, I'm happy that so many people
in Nigeria are interested in learning Java. So I have decided to run a couple of threads as
my contribution to developing a strong Java Community in Nigeria. So, if u are among the lucky
ones that have decided to get started with learning Java, never mind, i am here to just get
you started.
Learning Java could be fun and frustrating, depending on the angle you look at it
from.But I'm promising you that I am going to take it real slow and down to earth. I am also going to
go about it from the professional way i.e after finishing, if we ever finish, you should be
strong enough to add little effort and start hitting certification level. So let's get the ball
rolling with the requirements.

1. To learn Java, of course you need a Java Development Tool (jdk) now called J2SE (Java 2 Standard Edition)
from 5.0 version (Code named Tiger). There is a lot of improvement in the new edition, in fact there is a
new version (Code named Mustang) already out but still at a beta (development) stage, the final version
should be out soonest. But be rest assured that it is backward compatible. But Version 5.0 is recommended.
It can be downloaded, which ever version you need from this link.

http://java.sun.com/j2se/1.5.0/download.jsp

It is recommended to use Sun Download Manager (SDM) to download the J2SE else you are going to have a frustrating
time downloading it. The SDM can be downloaded from this link and it's easy to use. Read the read me file after
installing it to get cracking.

http://www.sun.com/download/

2. Next, you are going to need a java aware text editor, i will recommend TextPad, there is a free evaluation
version you can use. I do not recommend using Integrated Development Environment (IDE) for now. They do shield you
from the real details of the language, and more so, they will always add some IDE specific codes to your application,
this might confuse you. Also debugging your application could be difficult, if you don't know how errors are handled
in java. TextPad can be downloaded from this link.

http://www.textpad.com/download/

3. Now that we have all the needed software requirements, installing the J2SE easy for windows but for Linux
you have to do some tweeking to get it and running.For Linux users, if you are unable to install it, please
feel free to post your problems, promise to sort it with you. Next thing is to configure our system and
development environment. You need to add java to your system classpath. If you don't know what is classpath,
never mind, i will explain. It's just a way of telling the system where to look for executable commands. Like
if u type "dir" in your DOS prompt, the system list the content of a directory, because DOS commands are added
to the classpath by default. So let's set the classpath.


a. Right click My Computer icon on the desktop.
b. Select properties.
c. On the System Properties dialog box, select Advanced tab.
d. Click on the Environment Variables button at the bottom.
e. On the System Variables box, select Path under Variables, click Edit button.
f. An Edit System Variable dialog box will show.
g. In the Variable Value text Field, move your cursor to the beginning and add the path to
your J2SE bin folder. eg

C:\Program Files\Java\jdk1.5.0\bin,.

click all the OK to take you back to Environmental Variables dialog box. Here, we are just going
to add another simple System Variable, it for tools that depend on java to run. so
Click the New button, A new System Variable dialog box appears. Just fill as stated below.

Variable Name: JAVA_HOME
Variable Value: C:\Program Files\Java\jdk1.5.0 - don't add the bin folder

after this you can click all the OKs. Be warned, not to remove anything from the path when editing, if u do,
your system might become unstable. So be careful. So, we are through with that. O boy no give up ooh.

To test if everything went kool, click start, run, type cmd and hit enter. Na just to open Dos prompt o.
Type javac
hit enter, you should get a message like this.

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\Omo>javac
Usage: javac <options> <source files>
where possible options include:
-g Generate all debugging info
-g:none Generate no debugging info
-g:{lines,vars,source} Generate only some debugging info
-nowarn Generate no warnings
-verbose Output messages about what the compiler is doing
<more lines here>


If you get this message all de kampe. If you don't get this message, no yawa, some systems might require a restart,
so do it, if yawa still gas, ma boy, sorry you have to go all over the process again. It's never been easy, getting
it right the first time.

4. Na wa o. I bet you, this is going to be the longest part, we will ever get. It's nice we learn to get it right from
the beginning. Don't worry, this is the last paragraph for today. Setting our development environment. Java has
a recommended file standard structure you should follow, for now we will be doing it ourselves.But in real production
where you have hundreds of sources and class files, you will be using tools like Ant to arrange your file structures. I will just
list the structure.

a. Create a project directory that will contain all our projects folder.

C:\project

b. Create a sub directory, let's call it lecture1 (initial small letter), the name of our current project.

C:\project\lecture1

c. Create a sub folder for lecture1, name it src - it must be named src, source codes (what you write) goes into this folder.

C:\project\lecture1\src

d. Create another sub folder for lecture1, name it classes - must also be named classes and your class files(compiled code) sit here.

C:\project\lecture1\classes

So now we are ready to start the party, but before we go, let's look at area where most beginners encounter problems.Take note.

1. Java is highly type checked. Mean the javac (compiler) will make sure you follow the rules. No short cuts.

a and A are not the same. lagos and Lagos not same, so Lagos must be Lagos throughout your code.

2. White space are ignored. That is spaces between statements except for few exception like in classes,methods and
variables declaration. (if you don't understand, don't panic, we go jump am pass).

3. Class declaration must start with { and end with }.

4. Method declaration must have () immediately after it's name and like classes must start and
end with {}.

5. Every statement must terminiate with ;

Though there are more, but these are what i feel are the most common,
So my boy, me i dey check out. Take your time to digest it and make effort to get the required tool, because
by next class we will write our first program and explain some concept in java using a simple program.
Wish you all the best. To all, including the gurus and alike, please your criticism,observation,contribution and
recommendations are welcome.

Recommended free training site. Highly rated.

www.javaranch.com

Recommended Text book

HeadFirst Java 5.0 (Second Edition) by Kathy Sierra and Bert Bates.
HeadFirst Java (First Edition - covers version 1.4) by Same authors

Recommended books for Certifications.

Sun Certified Java Programmer

Sun Certified Java Programmer 1.4 Exam Guide by Kathy Sierra and Bert Bates.
Note:
The 5.0 version seems not to as good as the 1.4 version

Sun Certified Java Associate

no books yet. It's a new exam for entry level.

Sun Certified Web Component Developer 1.4.

HeadFirst Servlet and JSP ( rated best in the category) - lots of hands on practice
- simulation of real development paractice

Sun Certified Business Component Developer 1.3.

SCBCD EXAM STUDY KIT by Paul Sanghera (free pdf version available on-line)
EJB Specification 2.0 from Sun.
HeadFirst EJB by Kathy Sierra and Bert Bates (Very good teaching approach but some error, corrections available on-line).
Mastering Enterprise JavaBeans 3rd Edition by Ed Roman and co (free pdf version available on-line)

Recommended Bookshop in Lagos.

Ebuy (Prices are ok, extra 1k or 1.5k above on-line prices).
Delivering within 2 to 3 weeks.
Call Seun 01-4751491 or
Dolapo 08029494655

This is for Linux and Unix related system users. Here, am going to
demonstrate how to install and configure java on a Linux box, Stand easy and look this way (Drill Instructors - NYSC Camp).
For the development environment ,it's the same with the window's version except in instead of \ use /. Download whatever version (J2SE)
you need (either the bin or rpm). For me i prefer the binary (bin) version. With it i can have multiple version of J2SE on my
box, and with just a command i can switch between versions. But not possible with windows, this is Linux world.
I recommend install J2SE (j2sdk) in your \usr\local directory, so that you can make it available to all users of the Linux box,
that means you have to login as the root user. So copy the whatever J2SE version you downloaded to the /usr/local directory.

1. Open a terminal and CD to /usr/local
2. Make sure you have copied the J2SE file (ie downloaded bin file) to this location
3. Change the bin file permission

chmod 755 <j2se file name>.bin

4. Execute the bin file.

./<j2se file name>.bin

The installation process kicks off. Follow the instruction on the screen, and you might try saying no to the agreement.
but if you say yes, remember Ukwa (Agreement na Agreement o). All after the agreement and inflation of files. Check the
/usr/local you should find a folder name <j2se name> or it might have the old name ie j2sdk<version>.

5. Assume all is OK till now. Back to the terminal, create a system link to a jdk folder. If you don't understand
just type in this command.

ln -s /usr/local/<new j2sdk file name> /usr/local/jdk

After you run the command, check /usr/local directory, you should see a folder with a green arrow pointing up and named jdk.
this is the link we will use to set our classpart, so that if we have multiple version of J2SE, we simple issue same command
in 5. we just change the j2dsk file name to our required version.

6. The final stage, we need to add the tools to our classpath, OK don't worry, it isn't difficult. Follow me, I be old soldier
mind you. OK quick march.

7. Open the /etc/profile file using any text editor, some many available on Linux box. For me i use either kedit or gedit. so do this.
Still on the terminal.

gedit /etc/profile

8. Add this lines to the file,

export PATH=$PATH:/usr/local/jdk/bin:/user/local/jdk/lib/tools.jar:/usr/local/jdk/jre/lib/rt.jar:./
export JAVA_HOME=/usr/local/jdk

9. Save the file and exit.

10. Back to the terminal, type this command

source /etc/profile

This is to reload the new changes made in the profile file. And finally type javac at the terminal and will see
an output like the windows output. So Linux boys can now be part of the train. Please refer to to my conclusion on
on the last post. After this stage, nothing like windows or Linux version. This is JAVA platform independent.
.

I don't really understand this idea of asking students of Java to struggle with the command line when there's a free IDE called Netbeans! Sbucareer also happens to have a similar thread titled "Java Programming For Dummies". Java is so hot, isn't it?

Seun, i usually don't advice beginners to use IDE for some obvious reasons. Using the jdk tools allow learners to focus on the language, rather
than having to learn how to use an IDE. IDEs don't have specification as such anybody is free to develop it which ever way he or she likes.
IDEs do always add IDE specific codes to your source codes, so with no standard, how do explain these codes to a student.

There is always a mode in which you can create a blank .java file, write what you want to write, and compile! I agree that when you struggle with command line IDE may be easy but why struggle in the first place?

IDE these days are not as simple to use as you think. Personally, i started using IDE late last year. Imagine setting up your
class files to support import statements in your codes. Also, think about classpath issue to mention a few. For a beginner, that's just going to be too much. Another point is that when does he start learning to know the in and out of the compiler, like passing command line arguments, another hill for him. I think the use of IDE should be to enhance productivity, is like putting a fresh pastor in the pulpit, without giving him a bible. Even if he know where the verses are, do you expect him to cram the contents. No way brother. In fact, it is difficult to run away from command prompt as a java programmer. Like i read in one of the threads, somebody got a java file (jar) and wasn't able to run it, and his conclusion was java was difficult. To do that is quite simple. I will putthe command here for others, who are following. To run a java jar file use this command.

java -jar NameOfFile.jar --------- use the file name or complete file path

Momoh-mi, am in for this, please go on teaching, am learning

I second that. please don't mind my distracton. Carry on with your tutorials!

In the last tutorial, we looked at how to install and configure our Java environment on
both windos and Linux systems. We also looked at how to setup the java development environment
as required in real world production.
So, today, we are going to use a simple program to illustrate the fundamentals of java.
When you write a java program, what happen after that.What role those the compiler play, what is
a Java Virtual Machine and what does it do and how does it read your applications.So, we kick off
with the program as shown below. Please note the file name and the class MUST the SAME. And
must be saved with a java file extension ie
MyFirstApp.java as shown at the bottom of this post. Ok, pause, look at at the example.


Now think of development environment. We need to create a folder, the name should be the same with our project name.
This is not required but recommended. So our file structure should be like this.

C:\projects\nairaland

C:\projects\nairaland\src - put MyFirstApp.java here

C:\projects\nairaland\classes - put nothing here, we will tell the javac (compiler) to put thing here for use

C:\projects\nairaland\docs - nothing here, we will beg javadoc to help us too

Now we are done. Remember the rules, no IDE and Never compile from the editor. If you do i will know but won't tell
how. So, open the dos prompt.Go to our nairaland project folder.

C:\projects\nairaland - we all should be here, am right,if you are not here, please better be
"so thing is about to happen"

Let's compile the Application. Do this.


C:\projects\nairaland>javac -d classes src\MyFirstApp.java

C:\projects\nairaland> - if everything is ok, we are back here.

First thing just happend. Check the classes folder and what happened there. Please let me know.
If you missed the first please don't pass here, until you are sure you saw what happened.
If you are here, let's see another thing happening. So do this.



C:\projects\nairaland>javadoc -d C:\projects\nairaland\docs -keywords -author -v
ersion src\MyFirstApp.java

You will see all this stuffs, don't panic, it just doing what we ask it to do.

Creating destination directory: "C:\projects\nairaland\docs\"
Loading source file C:\projects\nairaland\src\MyFirstApp.java,
Constructing Javadoc information,
Standard Doclet version 1.6.0-rc
Building tree for all the packages and classes,
Generating C:\projects\nairaland\docs\com/nairaland/\MyFirstApp.html,
Generating C:\projects\nairaland\docs\com/nairaland/\package-frame.html,
Generating C:\projects\nairaland\docs\com/nairaland/\package-summary.html,
Generating C:\projects\nairaland\docs\com/nairaland/\package-tree.html,
Generating C:\projects\nairaland\docs\constant-values.html,
Building index for all the packages and classes,
Generating C:\projects\nairaland\docs\overview-tree.html,
Generating C:\projects\nairaland\docs\index-all.html,
Generating C:\projects\nairaland\docs\deprecated-list.html,
Building index for all classes,
Generating C:\projects\nairaland\docs\allclasses-frame.html,
Generating C:\projects\nairaland\docs\allclasses-noframe.html,
Generating C:\projects\nairaland\docs\index.html,
Generating C:\projects\nairaland\docs\help-doc.html,
Generating C:\projects\nairaland\docs\stylesheet.css,

C:\projects\nairaland> - so we are back here again.

Now go to docs folder.

C:\projects\nairaland\docs

whao where did the resources,com folders and the html file come from. Lession 2, let me know.

Finally to run MyFirstApp. Go here (dos prompt)

C:\projects\nairaland

type this command



C:\projects\nairaland>java -classpath classes com/nairaland/MyFirstApp

Learning Java Programming Without Tears at Nairaland.com - So this is the result of application

C:\projects\nairaland>

Take a look at the code,documentation and all the commands (dos), figure out our they relate.
Please do this before my next post. Remember, promised to be slow.

So many things and so many guestions a guess. Q and A next.

Stunts Corner.

For people with --- never mind let's try somethings.

1. Delete the docs and classes folders. Don't worry just do it.
2. Run the javac command again. ie

C:\projects\nairaland>javac -d classes src\MyFirstApp.java

C:\projects\nairaland>javadoc -d C:\projects\nairaland\docs -keywords -author -version src\MyFirstApp.java

As you can see you can actually use the java command tools to auto generate and package our codes.
Next, i want us to look at the documentation, compare the contents with our source code (MyFirstApp.java).

Remember promised to keep my notes short. As we progress, i will be introducing some of the new 5.0
features. Same application but in 5.0 way. The code is show below, follow the same procedure for
compilation and running the application. To generate the documentation, use a wild card (*) for java.

(go key in the the code, it's shown below and come back)

Javadoc command:

C:\projects\nairaland>javadoc -d C:\projects\nairaland\docs -keywords -author -version src\*.java

check the documentation to see the result.

Please try and run these examples, so that by next post, we will be speaking the same language.
Java

Hi mimoh_mi, good initiative, I want to join your Java class. I have a PC at home not connected to the web though so how do I download the J2SE, would I be able to download it into a 256MB flash drive? I go online from cafes and the owners don’t look kindly to people downloading stuffs on their systems. Could I get the software from Ikeja?
Thanks for the time and effort you are putting into this, I have just saved this page and would print it as soon as I get home!!

What is the purpose of Java , what and what is it for. How can be using it to process create stuff?

I am novice at Java, I just that i use it to play games

please

java is the best thing that happened to the world of programming.
Its a world on it own.

Hi All,
Let's take a look at our last two examples. Starting with the first.
From line 1 - 12 : these are all bunch of comments. Some text editors like TextPad
are able to identify comments. As you can see it appear in GREEN colour.

Line 14 : This is called package statements. It allow developers to arrange the source
codes in directories. The name must match a path to the specify directory. Most time the root
directory for java application is the classes directory, so you don't add it to the package statement.
If used in a code, it MUST be the first executable line, no other things are allowed before it except
comments.

Line 16 - 21: These are Java Documentation statements. Used by javadoc tool to generate
Documentation that describe the purpose,classes,methods and variables defined in an application.
But here, we are just describing the version and author.

Line 23 : This is the beginning of our class definition, from where object of this class
will be created for future use.

Line 32 - 36 : Shows a method definition. But the define here is a very special method in
Java. All java executable application must define it as it is is(public static void main(String[] args)).
This method is what the JVM uses to execute your application. eg when we say

java MyFirstApp

The JVM first look for the main method, accept the class name of the application as an arguments.
Usually as String array (more on this later).If everything is fine, it start running your logic.

So next let's look at the second code, will just explain the difference.

1. The static import statement(this is the name Sun called it), was introduced with 5.0.
It allow you to import static classes. It just a way of saving typing time. Once a static
class is imported, you can call it's method without specifying the fully qualified name. But, there
is danger hanging here. Assuming you have two methods with the same name but belonging to different
static classes, you have no option than to use there fully qualified name, else naming conflict(error).

2. the printf() : This was also added to version 5.0. Provide a very flexible way of formating
the output from your application. More on this later.

Let's look at the documentaion, you will notice that a method named ,

MyFirstApp()
MyFirstApp2()

This are special methods in java, the are called CONSTRUCTORS, this is what is what allow you
to create the object of the class. It must have the same name as the class name, it can not
return anything even void (more on this later) but can take arguments, usually what you will use
to initialise the object. All java class must have a construcutor, if you don't specify any, the
compiler will just be kind enough to add one for you (default). But if you do, then it must
follow the rule stated above. Also not that, if you do specify, the compiler won't bother to
create any for you.

3. Still looking at the documentation, you will see

Methods inherited from class java.lang.Object

This shows that your class extends Methods java.lang.Object, All classes in java extends
this class,thus automatically inherite all it's methed. note that java does
not support multiple inheritance like C 0r C++.


So, the next step is to download the java documentation API (Application Programming Interface).

http://java.sun.com/j2se/1.5.0/download.jsp
It contains all the classes definitions. Most of the times, this is what you are
going to be using in developing your applications.

Next post, we will be looking at the composition of a java class and get
ready for some hands-on.

hey, u r too good to be true. y r u doing this? i really do appreciate this. i'm studying IT in the uk. though i just started, i kinda farmiliar with java. can we do this one on one? my email is obinnaoji@hotmail.com. many many thanks

Am really sorry for the network break. For some of the questions asked, promise to post reply
by weekend. Why the break ? Noticed most people are having problems, getting the Java SE.
So, am compiling a java resource cd for anyone interested. The collection include best selling
books in java and related technologies such as Java Studio, JBose,Apache tomcat, Sun Java
Application server 8.0 and 9.0 to mention a few.
Am bases in lagos, so if you are in lagos, just indicate so that i will know how many
copies to make available. ALL THESE FOR FREE.

@MImoh_mi

i also reside in Lagos, I've been have a gr8 deal of prob getting the SDK been doing night browsing just to download the stuff at the end of the day, i dont get the file working. even right now 1:33am and still downloadind the SDK with the dowload manager just hoping it works.

I will appreciate it if i can get those resources. as soon as possible. cos right now am using JVM bundle with dreamweaver to compile my codes.

I reside in Ikeja/Ketu.
Thank Man.

mimoh_mi:

Am bases in lagos, so if you are in lagos, just indicate so that i will know how many
copies to make available. ALL THESE FOR FREE.

Thanks Mimoh_mi,
I am interested. Although I reside in Ibadan, I come to lagos twice a week and have a contact office in lagos Island.

@ mimoh

Thanks for your training. i love java but, i just dont have the time to really learn it.
I stay i lagos and i will need a copy too. how can i get it?

Please i tried to add the path it is not working.kindly look at what i did and see if there is an error

C:\Program Files\Java\jdk1.5.0\bin,.%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;C:\Microsoft SQL Server\80\Tools\Binn\

plz send the reply to this post or my email jebrills_jevic@yahoo.co.uk. i have install the jdk 1.5.0 even the sun application server



In the Variable Value text Field, move your cursor to the beginning and add the path to
your J2SE bin folder. eg

C:\Program Files\Java\jdk1.5.0\bin,.

click all the OK to take you back to Environmental Variables dialog box. Here, we are just going
to add another simple System Variable, it for tools that depend on java to run. so
Click the New button, A new System Variable dialog box appears. Just fill as stated below.

Variable Name: JAVA_HOME
Variable Value: C:\Program Files\Java\jdk1.5.0 - don't add the bin folder

Infact am lost, well pls u making it difficult, u can easily break it down to the slimplest format

thanks.

mimo mi

u deserve a national honour. I am am dumbfounded.

I am a Software tester, what materials can i use for to prepare for the Sun Certified Java Assocoate.

It's always good to learn something using the bare basics. That way, any "upgrades" end up being a plus. For example, I started web dev during the "dark ages". For the longest, I used notepad. I remember when IDEs became the in-thing. When asked at an interview what I used, when I told them notepad, the expression on their faces was like

For the "notepad-like" IDEs, coding in those is okay by me. But when you get to (at least in my field) IDEs like dreamweaver, frontpage et al, I would strongly recommend against it. You really need to know how things come together, as opposed to producing bloated code, half of which even you as the author don't understand. In particular, wherever I have worked, any mention of graphical IDEs results in such resumes being tossed directly into the dust bin

Jebrills,

Assuming you did cut/paste from your classpath settings. I noticed you donot have a semi-colon affter your first entry. There should also be a ; after the period. The period is an indication to the Java interpreter to include the current directory.

C:\Program Files\Java\jdk1.5.0\bin,.


It should be
C:\Program Files\Java\jdk1.5.0\bin;.;

Hope this helps.


BTW, excellent work mimoh!

jebrills:

Please i tried to add the path it is not working.kindly look at what i did and see if there is an error

C:\Program Files\Java\jdk1.5.0\bin,.%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;C:\Microsoft SQL Server\80\Tools\Binn\

plz send the reply to this post or my email jebrills_jevic@yahoo.co.uk. i have install the jdk 1.5.0 even the sun application server

As for using IDE's VS not using it, it's highly recommended, that beginners NOT use an IDE. It will shield you from a lot of the basics that are supposed to help solidify your knowledge. I started with notepad myself, until I came across textpad about 6 years ago or so. Textpad is one of the best basic text editors out there. It's also a big plus that it also works will with the Java compiler and interpreter. You can compile and run your Java applications and applets right there within textpad. Even if you need to pass arguments to main(). All the shops I have worked at use IBM's websphere studio. But, most of us also have  textpad on our machines. It's just one of the best editors out there. Best of all, it's a very small "free" download that installs in about a minute. Once you've mastered the basics, and you are ready for rapid development, than you can move to an IODE A very good free IODElike eclipse will serve you well in that area.


BTW, Not sure if mimoh mentioned this already, to compile/execute your apps via textpad, make sure you install the JDK before installing textpad. Because, during installation, textpad automatically searches (it does so ONLY during installation) for the java compiler and interpreter. If it does not find it, it will not perform the necessary setup to allow you to compile/run via textpad.

One of the best sites out there that will really help is, as mentioned by mimoh, javaranch.com. There are several forum there just visit the one appropriate for you. As a long time java professional, whenever I have any questions, javaranch is the first place I post to, before even trying google. So, please bookmark it and just go there to read the questions/responses in the forum of your choice(probably the beginner forum in this case).

Just got this post, but its truly interesting. Progress, pls!

Hello to all. First my apology to all for the long break, but thanks
to skima, who gave me a call that my fans are growing. So I promised him
to continue. While out. i have been laying my hands on new features of Java.
From IDEs to some fantastic libraries. So today i am going to look at a fundamental
aspect of programming VARIABLES.
Everything we ever do in any programming hangs around data. Variables are just
place holders , say we want to represent say name of employee, we must first declare
a variable to hold that name, from there we are free to manipulate it in any way within the
same program or from other programs.
Like any other programming language, Java has it's owm ways of handling the different
type of data. What is very important to us, is knowing the types and how they are being handled
as this will enable us to chose the right type of variables to represent our data. Let me quickly
list the data types we have in Java.

1. Byte (byte) -----> 8 bits Range --------> -128 to 127
2. Short (short) ------>16 bits --------> -32768 to 32767
3. Integer (int) -------->32 bits --------> -2147483648 to 2147483647
4. Long (long) ---------->64 bits --------> -9223372036854775808 to 9223372036854775808
5. Double (double) ------->32 bits -------> this is floating points (Home work, find float min and max values)
6. Float (float) ------->64 bits -------> do same for this
7. Boolean (boolean) ----> represent True or False
8. Character (char) -----> used to represent single characters. (basically int under the hood) --> range 0 to 65535.

These are the basic data types we have in Java, they are called PRIMITIVE Data type
and each have it's own range as shown above and default values as we will see later. Why must we know the range ? Please post
your answers here. Ok, let's play with these data types.


// This application is to show the default values of Java primitive data types

public class VariablePlay {

/**
By coding standard, variable names must start with small letter.
You must also know that the name of primitive data types are keywords
in Java, as such you can use them to to declare your own variable, method
or class names.
**/

// Here am just going to declare them, without initialisation
// the compiler will do that for me.
// The law say you can do this only for class variable
// more on that later

// things on the left are the data types and right the variable names
byte myByte;
short myShort;
int myInteger;
long myLong;
double myDouble;
float myFloat;
char character;
//Here let's add a char and initialise it
char initChar = 100;
boolean myBoolean;

/**
Let me just add a constructor, but if I don't add, the compiler will do it for \
me. If you don't declare one, the compiler adds a default constructor for you.
more on that later.Note same name with the class name and no return type
**/

public VariablePlay() {

//Let output something here to show when this constructor is called

System.out.println("I am VariablePlay Constructor , never mind";
}

//This our main method, entry method for our program

public static void main(String []args){


// Am just going to instantiate my class(make an object of the class and call it vp)
VariablePlay vp = new VariablePlay();

//use the object created ie vp to print out the default values
System.out.println("Default Value For byte = " + vp.myByte);
System.out.println("Default Value For short = " + vp.myShort);
System.out.println("Default Value For Interger = " + vp.myInteger);
System.out.println("Default Value For long = " + vp.myLong);
System.out.println("Default Value For double = " + vp.myDouble);
System.out.println("Default Value For float = " + vp.myFloat);
System.out.println("Default Value For char = " + vp.character);
System.out.println("Default Value For char = " + vp.initChar);
System.out.println("Default Value For boolean = " + vp.myBoolean);

}
}



Result :

I am VariablePlay Constructor , never mind
Default Value For byte = 0
Default Value For short = 0
Default Value For Interger = 0
Default Value For long = 0
Default Value For double = 0.0
Default Value For float = 0.0
Default Value For char =
Default Value For char = d
Default Value For boolean = false

Note:
1. the first four have default values of 0. All of these are basically int
2. The two output for char has nothing and d. char is unsigned (Can only be positive number)
3. boolean has false, used to test conditions
4. Float and double represent floating point number ie decimal
5. All numeric data type are signed in Java(ie can hold positive or negative values) except char.

For the Home work, take a look at the Java API Specification, each of these data type have a class
use them to get the maximium and minimium values of each. Just try, no matter you answer post it.

Hi, i think i need to get this classpath of a thing clear for windows users with this post.
Ok, right click on my computer and click properties from the drop down menu items.
I have tried to number the steps. I used my own computer path, yours might be different,
all the same it must point to the Java SE location on your computer.
I hope this will help.

Sorry just want to cover up for the lost time, so here is my solution to the home work
I will be looking forward to other solution. Yours might just be better than mine.


// Solution to the home work
// if you haven't tried it, please do

//Notice no public in class decreation
// more on that later
class MinMax {

/**
*Am not going to declare any class (Instance variable)
*because they all aready have values.
*Take a look at the API, Notice
*each of these primitive types have a class
*and some static field. Static fields are Class
*variables that it shared among mulitiple class instances.
* I will demostrate that in the next code
**/

//static byte byteMin = Byte.MIN_VALUE;



public static void main(String []args){
/**
*So just going to output the minimiun and maximium
*values of all the primitive data types.
*Notice I just use the class dot the value fields.
* static fields for you
**/

System.out.println("Minimium value of byte is "+ Byte.MIN_VALUE);
System.out.println("Maximinm value of byte is "+ Byte.MAX_VALUE);
System.out.println("Minimium value of short is "+ Short.MIN_VALUE);
System.out.println("Minimium value of short is "+ Short.MAX_VALUE);
System.out.println("Minimium value of int is "+ Integer.MIN_VALUE);
System.out.println("Maximinm value of int is "+ Integer.MAX_VALUE);
System.out.println("Minimium value of long is "+ Long.MIN_VALUE);
System.out.println("Maximinm value of long is "+ Long.MAX_VALUE);
System.out.println("Minimium value of double is "+ Double.MIN_VALUE);
System.out.println("Maximinm value of double is "+ Double.MAX_VALUE);
System.out.println("Minimium value of float is "+ Float.MIN_VALUE);
System.out.println("Maximinm value of float is "+ Float.MAX_VALUE);

//Here we need to do some extra work to get the min and max value
System.out.println("Minimium value of char is "+ Character.MIN_VALUE); // prints blank
System.out.println("Maximinm value of char is "+ Character.MAX_VALUE); // prints ?
System.out.println();
System.out.println("About to do the tricks of getting the minimium and maximium values of char";

/**
* To print the minimiun and maximium values of char can be quite tricky
*Remember char is just init under the hood.
*We got the value ----> Character.MIN_VALUE
*Passed the value to the Character.valueOf(Character.MIN_VALUE)
*Change th result to interger (int)Character.valueOf(Character.MIN_VALUE)
**/



System.out.println("Minimium value of char is "+ (int)Character.valueOf(Character.MIN_VALUE));
System.out.println("Maximium value of char is "+ (int)Character.valueOf(Character.MAX_VALUE));


}
}


Result

Minimium value of byte is -128
Maximinm value of byte is 127
Minimium value of short is -32768
Minimium value of short is 32767
Minimium value of int is -2147483648
Maximinm value of int is 2147483647
Minimium value of long is -9223372036854775808
Maximinm value of long is 9223372036854775807
Minimium value of double is 4.9E-324
Maximinm value of double is 1.7976931348623157E308
Minimium value of float is 1.4E-45
Maximinm value of float is 3.4028235E38
Minimium value of char is
Maximinm value of char is ?

About to do the tricks of getting the minimium and maximium values of char
Minimium value of char is 0
Maximium value of char is 65535

So let take more look at variable. In Java we have basically two types of variable reference ie
Object Reference (ie a reference to a class object) and Primitive reference, which we look at yesterday.
Hope, thing are not getting bored. Let's also talk about a typical class structure.I will show it now.


class ClassName {

// Every class must have a name and defined using the class keyword
// The can also have other modifier like public etc that shows
// how we intend to expose our class to other applications or classes
// either wihin our project or the outside world.
// Naming Rules
// 1.Must start with a letter, underscore( _ ) or dollar sign ( $ ).
// 2.Can only use number after the first Letter.
// 3 Must not be Java Keywords, keywords are used by the compiler so
// the are special words.


// classes can contain class variable

datatype variableName;

// if you don't want the default values for class variables, you specified a you
// own default value.
// Remember, they can either be primitive or object reference variables.

datatype variableName = initialisationValue;


// classes can have multiple constructors, this a place to initialiase class
// variables


public ClassName() {

// Constructor are just special methods
// Ther are used to create object instances
// Naming rule --> must be same name with the class name and can have diff
// access modifier
// This is called default constructor because they don't take any argument
// If we don't specify ANY constructor, the compiler will alway be kind to
// inject one for you.




// let me just show how a class with multiple constructor look like.

public ClassName(int anumber){
// this one takes a number an argument
// to invoke it you must pass an int to it eg ClassName cname = new
// ClassName(0); will explain this later

}


// The next thing in a class are methods

modifier returnType methodName(dataType argument) {

return returnType; // Arguments reurned must be same with the
// returnType dataType;
}
public int addTwoNumber(int number1, number2){
// Methods contains actions you want to perform on the variables
// Here we want to add two numbers number1 and number2

// Naming convection same as class
// Must have return type - must return a result
// Like here, we are returning an integer (int)

return number1 + number2;

}

// Every Executable Java Class must have a main method
// Notice the the structure, any attempt to change it, the code will compile but
// will not run
// because the JVM, looks for this method to run your application.

public static void main(String [] args){
// It must take an arrray of String as argument, must be public, static and void
// return type


// Here we can start our program

// Instantiante the class (create an object of the class)

ClassName cname = new ClassName();
// the new keyword is used to create a new object of a class
// Here we created an instance of a class using the default
// constructor

ClassName dname = new Classname(20);
// Create another object of ClassName, Using
// the ClassName(int) constructor

// we can now call our methods

cname.mehodName(); cname.addtwoNumber(20,30);

// using dname instance

dname.mehodName();
dname.addtwoNumber(20,30);

} // end of main method

}// end the class defination

So, this is a complete description of a class structure. In all of our lives as programmers. this is all we are ever going
to be writing. The difference now is understanding the logic and putting it into this structure, infact this is a class
template.

I hope to finish the variable trail by next post, so that we can move to methods.