Introduction to java

Say Hello to Java
1
Rakesh Kumar Singh

Say Hello to Java
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Introduction
Java Technology Structure
Installation instruction of JDK 5.0
JDK directory structure
Bin
Lib
JRE, etc
Steps to Develop Java Program
Composing
Compilation
Running
Developing Simple Java Program
Case 1: From bin folder
Case 2: Outside of bin folder
Case 3: .java and .class files in separate
location
Questions

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Introduction
To develop any java program we require software, it’s called
J2SDK (Java 2 Standard Development kit)
Or
J2SEDK (Java 2 Standard Edition Development Kit)
Or, Most Commonly its known as
JDK (Java Development Kit)
Now, the main component of JDK is
J2SRE (Java 2 Standard Run Time Environment)
Or
J2SERE (Java 2 Standard Edition Run Time Environment)
Or, most commonly called
JRE (Java Run Time Environment)

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Java Technology Structure
J2SE is base for all java technology. J2EE and J2ME both are
independent to each other but
Base of both streams (EE & ME) is J2SE.
J2SE
J2EE
Java 2 Enterprise Edition
J2ME
Java 2 Micro/Mobile Edition

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Installation instruction of JDK 5.0
Here we have to perform following task
 Change the location of installation from OS drive (Generally
C :) to any other drive.
 Don’t use space in any of folder or directory name
 Here we will see following Components
o Development Tools [Mandatory]
o Source [can be filter but don’t do it]
o Demo [can be filter but don’t do it]
o Public JRE [Filter this]
 Filter Public JRE(Don’t Install)
 Public JRE is used for production purpose so while
development we don’t require this.
 All these components will store or install at same location,
we can’t install different component in different location.
 We can’t filter Development tools while installing JDK.
Except this we can filter all components.
Download JDK 5.0
JDK 5.0 .exe
Follow the instruction
(Accept License)
Custom setup
Install
Finish
By default java will
install in OS drive. That
we should change to other
location.
Spaces in folder or dir name can
misguide to OS and other support
tools, so it’s not advisable to use.

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Installation Step by step:
JDK 5.0 exe
Double click on exe file
Processing screen will appear
It will take few minute to process.
After processing, License Screen will
appear where we have to accept the
license and proceed for next.
These screens are called wizard or
window
After license page, custom setup
wizard will appear where we will do
few modifications.
First we will change the installation
location from OS drive to any other
Drive using change option.
1

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When we will press change button
then this window will appear here
we have to change location and
then press ok button.
After changing location again
control will come back to previous
window, now here we have to
perform second operation which is
filter Public JRE for this purpose we
will click on public JRE and then
select don’t install this feature
option.
Now we are good to proceed for
next….
Now installing process will
start. This will take few minute.

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Congratulation!!! Java is successfully installed in our machine.
This is last wizard which will
appear when Installation will
complete successfully.

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Here important folders are:
Bin:
 Bin stands for Binary
 It keeps binary files
 Human can’t understand binary information, its machine
understandable codes.
 There are different file extension are there, files commonly used
extensions are:
.exe, .bat, .cmd, .class, .jpeg, .quicktime, .mpg, .mpeg etc
 The PATH environment variable should contain an entry for this
directory.
Lib:
 Lib stands for library.
 In java lib folder is used for to keep jar file.
 Jar stands for Java Archive.
JRE:
 Jar stands for Java Run time Environment.
 Provide platform to run java program.
 To run java program we require Run time Environment, JRE is
providing that environment to java program.
 While installation we didn't install public jre then also we will get
JRE folder. This is private JRE which comes along with
development tools.
 Private and Public JRE:
Private JRE is mainly for development purpose.
Public JRE is purely for production purpose.
 JRE is separate software.
 JDK is built on the JRE.

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JDK = JRE + other concept
Src.zip
 Src.zip contains the source code of JDK.
 Whatever code is developed by Sun is present here
 We can check internal implementation of Java.This is one of the
reasons because java is called as Open Source.
Sample
Include
Demo
JDK
Other Concept
JRE
Development Purpose
Running purpose
Other folder present inside JDK 5.0 Installation
Src.zip
Src
Java
Select folder and open it
We can see the source
code

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Steps to Develop Java Program
We can divide java program development in 3 cycles. These are
1. Composing
2. Compilation
3. Running

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Developing Simple Java Program
Case 1: Development, compilation, and running from bin folder of JDK
5.0
Step 1: Composing
I. Open Notepad (Default Editor)
II. Here we have to develop /write java program
III. Save the program inside bin folder as classname.java it means for
the above example file name should be Simple.java.
Extension should be .java for every java program
Composing step is finished.
The outcome of the first step is: .java file
Now we will move for next step.
class Simple
{
public static void main(String args[])
{
System.out.println("Hello to All");
}
}

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D:/JDK5.0/bin>javac Simple.java
Step 2: Compilation
Inside bin folder there are several command or .exe files are available. By
making use of these tools we can compile and run our java program. One of
common command file is
Javac: - javac is a command or tools use to compile java program
While compiling java program javac command will perform two tasks
1. Check each and every statement, that it is correct or not.
2. If it is correct then javac command will generate .class file for
corresponding to .java file
It means after successful compilation we will get .class file.
To compile or run java program we required Command Window
1. Open command window (cmd)
2. In command window go where our program is saved
Suppose it’s in D:/JDK5.0/bin>
Now we will fire command from here
D:/JDK5.0/bin>javac Simple.java
When we will press enter, first command window indentify javac
command then Second javac command will check program and
generate one .class file if program is correct.
Command is
So the Output of this stage is: .class file
Now we will proceed for the next step

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D:/JDK5.0/bin> java Simple
Step 3: Running
To run java program we have to use “Java” command/exe
Java: It is a command or tool present inside bin folder is JDK, use to
run/execute java program.
Java command require .class file.
Use of Java command to run our program
D:/JDK5.0/bin>java Simple
Here
Location where .class files is
available Command
Name of class

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Few Point to remember:
While running java file we have to write only name of class (e.g. Simple)
compiler automatic take .class as extension.
If we will keep .class file extension separately then compiler will treat it
as a class name and at last again it will add .class,
It will change the name of file, and our program will not execute.
So while running java programs only mention the name of File or class
Example
D:/JDK5.0/bin>java Simple [User Command]
Compiler will modify it and treat is as
D:/JDK5.0/bin>java Simple.class [compiler command]
Now, If we will write
D:/JDK5.0/bin>java Simple.class
Then compiler will again add .class at end and it will become
D:/JDK5.0/bin>java Simple.class.class
It is not correct so it will not execute successfully.

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Example 2: Java Program
Step 1: Composing
Save as: Basic.java
Location: D:/JDK5.0/bin>
Step 2: Compilation
Go to saved location (D:/JDK5.0/bin>) and compile the program
D:/JDK5.0/bin>javac Basic.java
Here after successful compilation we will get one .class file named
Basic.class on D:/JDK5.0/bin> location.
Step 3: Running
Go to location where .class file is present it means (D:/JDK5.0/bin>) and run
the program
D:/JDK5.0/bin>java Basic
Here after successful execution we will get output as
Hello World!
class Basic
{
public static void main(String[] args)
{
System.out.println("Hello World!");
}
}

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Case 2: Developing Java program outside to bin folder of JDK
Up to now we saved the program inside the bin folder, but it’s not proper or
advisable way to develop program.
 Saving program inside bin folder of JDK and compiling and
running from there is very simple any easy. But the problem is
 Bin folder of JDK is specific to keeping .exe file it’s should not be
use to keep .java and .class file their.
 We can save, compile and run the program from outside of bin
folder.
One better approach is to keep .java and .class file in different location without
touching bin folder.
Developing Java program outside to the bin folder of JDK
We want to compile and run our java program from E:/Lab/Dev but javac.exe
and java.exe are present in different location.
E:/Lab/Dev> javac Hello.java
Compilation fails
Javac.exe
Java.exe
D:/JDK5.0
bin
Hello.java
E:/Lab
Dev
All .exe/command/tools are
present inside the bin folder of
JDK5.0
We Kept our program inside
E:/Lab/Dev

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This will not compile successfully because javac present in different folder.
Description
When we will hit Enter button then command window will perform two tasks
Search/Identify Javac command
Execute Javac command
We are executing program from E:/Lab/Dev> location so command window
will search javac in present location. At the present location javac command
is not available so resultant compilation fails.
For successful compilation and Running we require updating Path
Environment Variable.
Some common path environment variables are
path
classpath
java_home
j2ee_home
ant_home
sql_home
Updating PATH environment variable
E:/Lab/Dev>set PATH=D:/JDK5.0/bin
Now if we will compile java program then
Now command window will check from which location I am running. In
this situation present working directory(PWD) is E:/Lab/Dev>
Then it will check javac command is present in current
location/batch/PWD or not. (E:/Lab/Dev> javac Hello.java)

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If javac command is not available on current location then command
window will check is there any PATH environment variable is Updated
their?
If it is their then command window control will go to Path environment
variable location and it will check javac command on that location.
If javac command is present their then it will identify it and execute the
java program.
Command window Job
Check command location
o Present location
o Path environment variable
Identify command
Run command
If we are setting the path environment variable then
First it will search particular/given command on Present Working Directory
if that command will not present on PWD then only
It will go and check PATH environment variable location.
Note: If we are setting PATH environment variable through/on
command window then sated PATH environment variable will be
available for only for that particular command window and when we
will close it then sated path will also destroy. It will be not available for
other command window.
Tip:
When we are saving any file then we should give file name in double
quotes “ ” with extension.
“File_name.extension”
It will tell to operating system that doesn’t add any default extension.
Generally default extension of any txt file is .txt or .doc.

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Set the PATH environment variable to bin folder of JDK5.0
We can set PATH environment variable from any location of
command window.
On Command window go to the location where java program is present.
Compile the java program
Here two tasks will happen
1. Command Window job
It will check from where I am running and
It will identify the javac command
2. Javac.exe command job
Check the given file name.
Check that at PWD its present or not
If it is present then it will compile and generate the .class file.
Similarly for java.exe command, when we will trigger java command on
command window then
 Command window job
Identify the java command
 Java.exe command job
Check the class name and then verify it and
At last execute it and produce the o/p.
While setting path we should write path in capital/upper case letters.
Writing path in lower case is proper but not advisable.
Writing path in upper case is convention not rules.

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>Set abc=123
>Echo %abc%; display the present path.
O/p 123
>Set new_env=%abc%
Here we are taking the value of abc and
putting in into new_env.
>echo %abc%
o/p 123
>echo %new_env%
o/p 123
>set new_env=%abc%;0000
echo %new_env%
123;0000
>set new_env=%new_env%;1111
echo %new_env%
123.0000;1111

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Sr.
No
Environment variable
Reading Env.
Variable
Result
1 set abc=123 echo %abc% 123
2 set abc=456 do 456
3 set abc=%abc%789 do 456;789
4 Set xyz=%abc%;1011 Echo %xyz% 456;789;1011
5 Do Echo %pqr% %pqr%
6 Set pqr=hello Echo %pqr% Hello
7 Set PATH=”D:/JDK5.0/bin” Echo %path% D:/JDK5.0/bin
8 Set PATH=D:/Mysql/bin do D:/mysql/bin
9 Set PATH=%path%D:/Mysql/bin do D:/JDK5.0/bin;D:/my
sql/bin
Here in this Table serial no 2 is an example of replacing the previous path
environment variable.
3 is an example of adding path environment variable.
Here ;( semicolon) is used as a delimiter. Here we can set any number of
locations in path environment variable in Path Environment Variable.
We can set same path many times.
>set Path=abc;
>set Path=%Path%;abc;
>set Path=%Path%;abc
Here in This example we are setting the same path 3 times. It is proper but not
advisable;
In this condition if any location is not present then compiler will check the
same location one after, it will time expensive for compiler.
If we will open command window first time and directly we will give
command
>echo %path%
It will print all pre-define path.

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My computer
Properties
New Path
Now we can add new path or replace the existing path.
Where is path environment variable.
Whatever path we are setting the path inside path command window is local
for that particular command window.
It will not affect the other or global path environment variable, Its local for
that command window.
If we want to set path globally then we can go for
Keep semicolon (;) between two path locations as delimiter for
separation.
We can set path Operating system wise through two ways
1. User Level (Specific to one user)
2. System Level (Global to System)
My Computer
Properties
Edit / new / path
Advanced

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User level Environment variable:
It is available for particular/specific user. If system has 3 user accounts then
we can set 3 path environment variables one for every user. These paths are
specific to user only these path are not accessible for other user. It provides
security.
System level Environment variable:
This is visible to all user here if we will set path then these path is available for
all system users. It is not advisable to use because it is not secure.
So we can implement PATH environment variable in three ways:
1. Command windows wise (Local to command window)
2. User level command window (local to one user)
3. System level command window (Global to system)
While setting the PATH through command window we should not use space in
between if we will give space before or after or in between then it will not
work as a PATH environment variable.
PATH=123 (Correct no space in between)
PATH =123 (Incorrect space is there in between )
PATH= 123 (Incorrect space is there in between )
So we should not use space after and before name and write it as a one
word.
It will execute successfully but it will not work as a path
environment variable because its path with space. Operation
system will treat space as a character
It will execute successfully but it will not work as a path
environment variable because its path with space. Operation
system will treat space as a character

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While setting path through my computer environment variable we
should not use space as before Path
If we will use space before writing PATH ( PATH) then it will not
work as a path environment variable.
If we will use path after space then OS will automatically remove
it.

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Case 3: Keeping .java file and .class file in different location:
In same directory it is not advisable to keep two different types of file
(e.g. .java, .class).
In Java we can keep different file in different location.
Save as: A.java
Location: D:/Dev/src/A.java
Open command window
If we will execute/compile normally then compiler will generate .class
file at the same location by default.
If we want to generate .class file in different location then we can go for
command
D:/Dev/Src>javac –d ../classes A.java
Here after compilation .class file will generate inside classes folder
D:
Dev
Src
Classes
A.java
A.class
Class A
{
public static void main(String args[])
{
System.out.println(“Hello”);
}
}

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So through –d option we can guide to the compiler to the generate the .class file
at desired location.
D:/Dev/Src>javac –d ../classes A.java
-d option
-d option will guide to the
compiler that don’t generate
.class file at the same location
generate it in given location
../classes
.. will guide to compiler to go one step
up then
/ classes guide to the compiler that
now search classes folder in present
location and generate .class file inside
this folder

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e.g. 1: D:/Dev/Src>javac –d .. A.java
e.g. 2: D: /Dev/Src>javac -d . A.java
e.g. 3: D: /Dev/Src>javac -d ../.. A.java
Here .. will guide to the
compiler that go one step up
from the present location
(present location is Src and
one step up means parent
folder of Src I mean Dev) and
generate .class file there
One . (dot) represents the
present working directory.
So here compiler will generate
the .class file at the same
location
It is similar to simple javac
command invocation.
../..
../.. move the control 2 step
up and generate .class file
at that location

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e.g. 4: D: /Dev/Src>javac -d sub A.java
e.g. 5: D:/Dev/Src>javac -d sub/pack1 A.java

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From present directory to its successive child folder or its parent folder
we can reach by using / (slash) and .. or by folder name.
So if we want to store or access .class file in different folder in the same
directory then we can go for .. and / (slash)
This is called relative path
We can access only one drive folder using Relative path.
Now if we will go for
D:/Dev/Src>javac -d ../../../../../../../../.. A.java
Here this command will not give error It will generate .class file in D: drive.
Using Relative path we can travel only in the present Drive only.
Using relative path we can’t generate .class file in different drive. We
can only generate .class file in that drive only.
If we want to access other Diver folder or want to save/generate .class
file from different Driver to different Drive the we can go for Absolute
Path.
Absolute Path:
Through absolute path we can travel anywhere in the system. In absolute
path we have to give the complete path of the location.
E.g.
D:/Dev/Src>javac -d E:/project/code/Classes A.java
In this example .class file will generate at E:/project/code/Classes.

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Table that showing location after compilation according to
the above diagram:
Sr No Command Invocation from E:/Lab2/Batch/Src Location of .class file
1 Javac A.java Src
2 Javac –d . A.java Src
3 Javac -d ..A.java Batch
4 Javac -d ../.. A.java Lab2
5 Javac -d ../Classes A.java Classes
6 Javac -d ../../A6 A.java A6
7 Javac -d A2/B2/../B2 A.java B2
8 Javac -d ../../Batch/Src/A2/.. A.java Src
9 Javac -d D:/XYZ/A1/B1 A.java B1
10 Javac -d C:/Lab1/A/B A.java B
So whenever we want to use directory or folder of same drive then we can go
for relative path or absolute path.
If we want to use folder or directory of different Drive then we can use only
Absolute path. Here in his situation Relative path is not possible.

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Tips:
If in address bar we are able to see only current folder name and we want to
see complete path then we can go for
Tools
Folder option
View
Select Display full Path
Ok

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Questions
1. What is the latest Version of JDK?
2. JDK stands for?
3. J2SE stands for?
4. Why exe files are used?
5. What is WIZARD?
6. While installing JDK5.0 will get four items, name them.
7. Which item is mandatory to install?
8. Which item is not mandatory to install?
9. Which item is used for development purpose?
10. Which item is used for customer purpose?
11. Which item is used for production purpose?
12. Which item has to be filtered while installing JDK5.0?
13. Why we will go for EXE files?
14. In which drive we have to keep the development software?
15. Why development languages are not kept inside the C drive?
16. What happens if we install the development language inside the C
drive?
17. Currently companies are using which version of JDK?
18. While installing whether we have to give space between JDK and
5.0(Y/N)
19. If we give space between JDK and 5.0 what happens?
20. If we don’t give space between JDK and 5.0 what happens?
21. bin stands for what?
22. What is the use of bin?
23. What kinds of files are kept inside the bin folder?
24. Which are the different types of binary files?
25. Whether binary files are readable by humans?
26. Which type of language is understandable by the computers?
27. Which type of language is understandable by the humans?
28. Name two types of file in bin folder.
29. Lib stands for what?
30. What does lib folder contain?
31. In case of java, what we call for lib folder?
32. What does lib folder contain?

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33. What does jar stands for?
34. Mention the type of jre.
35. Why private jre is used?
36. Why public jre is used?
37. Why we are filtering the public jre while installing?
38. What stands for jre?
39. jre is a software (Y/N)
40. Whether jre contains bin and lib files?
41. bin and lib files of jre are used for what?
42. For running the java programs which files are used?
43. Where .dll files are located?
44. What is rt.jar?
45. For what rt.jar files are used?
46. What does rt.jar file contain?
47. What is src?
48. What is wrar?
49. For what purpose wrar files are used?
50. In which condition we cannot open the zip file?
51. What we have to do if src is not in a proper format?
52. Whether wrar is used for developing software?
53. How we can unzip the src file?
54. Where .java files are located?
55. .java files are character based files(Y/N)
56. What do you mean by open source?
57. Why java is better than other languages?
58. What do you mean by composing?
59. How to open an editor?
60. How to open a command window?
61. Which command is used for copying?
62. Which command is used for saving the file?
63. In which location we have to save the java file?
64. What is the file name has to be given while saving the java program?
64. By giving which extension we can save the java program?
65. First letter of the class name should be in upper case(Y/N)
66. What happens if we are not saving the file name of java program
inside the double quote?
67. Which command is used for compiling the java program?

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68. Which command is used to run the java program?
69. What is compilation?
70. After compiling what type of file we will get?
71. What do you mean by ‘cd’?
72. Which are the two conditions occurred while compiling the java
program?
73. For what .java files are used?
74. For what .class are used?
75. What is the input for javac command?
76. What is the input for java command?
77. For javac command input is .class file(Y/N)
78. For java command input is .java file(Y/N)
79. Why we are not giving any extension to the filename while running
the java program?
80. Name common three types of binary files
81. Abbreviate J2ME.
82. Abbreviate J2EE.
83. What is meant by environment variable?
84.Why set command is used?
85. Why set echo is used?
86.Whether the environment variable value is lost while closing the
command window?
87. How to set the env-value in a command window permanently?
88. Where we have to go for setting env variable?
89.What is path?
90.How to set path environment variable?
91. If the java code is syntactically correct, then its binary code is stored
in which type of file?
92. What is the usage of set command?
93. What is the usage of more than one semi colon in the path
environment variable?
94.Updating of path in operating system itself is globally available to all
the command window(y/n)?
95. How to synchronize two different directory or drive location?
96.What is classpath?
97. What does command window do?
98.What is need to set the environment variable?
99.Which are the two ways of setting the path?
100.Name the two types of environment variable?
101. What do you mean by system variable?

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102.What do you mean by user variable?
103.What are the disadvantages of system variable?
104.What are the advantages of user variable?
105.How we can set new user variable?
106.How to update the path environment variable in operating stystem?
107.By using which command we can display the new and existing env-
var?
108.Before setting the path in operating system, is it possible to run the
command in the command window?
Always continue the climb. It is
possible for you to do whatever you choose,
if you first get to know who you are and
are willing to work with a power that is
greater than ourselves to do it.

Introduction to java

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