Chapter 1: Java Introduction
1. What is Java?
2. History of Java
3. Features of Java
4. Hello Java Program
5. Program Internal
6. How to set path?
7. Difference between JDK,JRE and JVM
8. Internal Details of JVM
9. Variable and Data Type
10. Unicode System
11. Operators
1. What is Java?
Java is a programming language and a platform.
Platform Any hardware or software environment in which a program runs, known as a platform. Since Java has its own Runtime Environment (JRE) and API, it is called platform.
Java Example
class Simple
{
public static void main(String args[])
{
System.out.println("Hello Java");
}
}
Where it is used?
According to Sun, 3 billion devices run java. There are many devices where java is currently used. Some of them are as follows:
Desktop Applications such as acrobat reader, media player, antivirus etc.
Web Applications such as irctc.co.in, javatpoint.com etc.
Enterprise Applications such as banking applications.
Mobile
Embedded System
Smart Card
Robotics
Games etc.
Types of Java Applications
There are mainly 4 type of applications that can be created using java:
1) Standalone Application
It is also known as desktop application or window-based application. An application that we need to install on every machine such as media player, antivirus etc. AWT and Swing are used in java for creating standalone applications.
2) Web Application
An application that runs on the server side and creates dynamic page, is called web application. Currently, servlet, jsp, struts, jsf etc. technologies are used for creating web applications in java.
3) Enterprise Application
An application that is distributed in nature, such as banking applications etc. It has the advantage of high level security, load balancing and clustering. In java, EJB is used for creating enterprise applications.
4) Mobile Application
An application that is created for mobile devices. Currently Android and Java ME are used for creating mobile applications.
2. History of Java
Java history is interesting to know. The history of java starts from Green Team. Java team members (also known as Green Team), initiated a revolutionary task to develop a language for digital devices such as set-top boxes, televisions etc.
For the green team members, it was an advance concept at that time. But, it was suited for internet programming. Later, Java technology as incorporated by Netscape.
Currently, Java is used in internet programming, mobile devices, games, e-business solutions etc. There are given the major points that describes the history of java.
1) James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. The small team of sun engineers called Green Team.
2) Originally designed for small, embedded systems in electronic appliances like set-top boxes.
3) Firstly, it was called "Greentalk" by James Gosling and file extension was .gt.
4) After that, it was called Oak and was developed as a part of the Green project.
Why Oak name for java language?
5) Why Oak? Oak is a symbol of strength and choosen as a national tree of many countries like U.S.A., France, Germany, Romania etc.
6) In 1995, Oak was renamed as "Java" because it was already a trademark by Oak Technologies.
Why Java name for java language?
7) Why they choosed java name for java language? The team gathered to choose a new name. The suggested words were "dynamic", "revolutionary", "Silk", "jolt", "DNA" etc. They wanted something that reflected the essence of the technology: revolutionary, dynamic, lively, cool, unique, and easy to spell and fun to say.
According to James Gosling "Java was one of the top choices along with Silk". Since java was so unique, most of the team members preferred java.
8) Java is an island of Indonesia where first coffee was produced (called java coffee).
9) Notice that Java is just a name not an acronym.
10) Originally developed by James Gosling at Sun Microsystems (which is now a subsidiary of Oracle Corporation) and released in 1995.
11) In 1995, Time magazine called Java one of the Ten Best Products of 1995.
12) JDK 1.0 released in(January 23, 1996).
Java Version History
There are many java versions that have been released.
1. JDK Alpha and Beta (1995)
2. JDK 1.0 (23rd Jan, 1996)
3. JDK 1.1 (19th Feb, 1997)
4. J2SE 1.2 (8th Dec, 1998)
5. J2SE 1.3 (8th May, 2000)
6. J2SE 1.4 (6th Feb, 2002)
7. J2SE 5.0 (30th Sep, 2004)
8. Java SE 6 (11th Dec, 2006)
10. Java SE 7 (28th July, 2011)
3. Features of Java
There is given many features of java. They are also known as java buzzwords. The Java Features given below are simple and easy to understand.
1. Simple
2. Object-Oriented
3. Platform independent
4. Secured
5. Robust
6. Architecture neutral
7. Portable
8. Dynamic
9. Interpreted
10. High Performance
11. Multithreaded
12. Distributed
Simple
According to Sun, Java language is simple because:
syntax is based on C++ (so easier for programmers to learn it after C++).
removed many confusing and/or rarely-used features e.g., explicit pointers, operator overloading etc.
No need to remove unreferenced objects because there is Automatic Garbage Collection in java.
Object-oriented
Object-oriented means we organize our software as a combination of different types of objects that incorporates both data and behaviour.
Object-oriented programming(OOPs) is a methodology that simplify software development and maintenance by providing some rules.
Basic concepts of OOPs are:
Object
Class
Inheritance
Polymorphism
Abstraction
Encapsulation
Platform Independent
A platform is the hardware or software environment in which a program runs. There are two types of platforms software-based and hardware-based. Java provides software-based platform. The Java platform differs from most other platforms in the sense that it's a software-based platform that runs on top of other hardware-based platforms. It has two components:
1. Runtime Environment
2. API(Application Programming Interface)
Java code can be run on multiple platforms e.g.Windows,Linux,Sun Solaris,Mac/OS etc. Java code is compiled by the compiler and converted into bytecode.This bytecode is a platform independent code because it can be run on multiple platforms i.e. Write Once and Run Anywhere(WORA).
Secured
Java is secured because:
No explicit pointer
Programs run inside virtual machine sandbox
Class loader- adds security by separating the package for the classes of the local file system from those that are imported from network sources.
Byte code Verifier- checks the code fragments for illegal code that can violate access right to objects.
5. Security Manager- determines what resources a class can access such as reading and writing to the local disk.
These security are provided by java language. Some security can also be provided by application developer through SSL,JAAS,cryptography etc.
Robust
Robust simply means strong. Java uses strong memory management. There are lack of pointers that avoids security problem. There is automatic garbage collection in java. There is exception handling and type checking mechanism in java. All these points makes java robust.
Architecture-neutral
There is no implementation dependent features e.g. size of primitive types is set.
Portable
We may carry the java byte code to any platform.
High-performance
Java is faster than traditional interpretation since byte code is "close" to native code still somewhat slower than a compiled language (e.g., C++)
Distributed
We can create distributed applications in java. RMI and EJB are used for creating distributed applications. We may access files by calling the methods from any machine on the internet.
Multi-threaded
A thread is like a separate program, executing concurrently. We can write Java programs that deal with many tasks at once by defining multiple threads. The main advantage of multi-threading is that it shares the same memory. Threads are important for multi-media, Web applications etc.
.
4. Hello Java Program
In this page, we will learn how to write the simple program of java. We can write a simple hello java program easily after installing the JDK.
To create a simple java program, you need to create a class that contains main method. Let's understand the requirement first.
Requirement for Hello Java Example
For executing any java program, you need to
install the JDK if you don't have installed it, download the JDK and install it.
create the java program
compile and run the java program
Creating hello java example
Let's create the hello java program:
class Simple{
public static void main(String args[]){
System.out.println("Hello Java");
}
}
save this file as Simple.java
To compile:
javac Simple.java
To execute:
java Simple
Output:Hello Java
Understanding first java program
1. Let's see what is the meaning of class, public, static, void, main, String[], System.out.println().
2. class keyword is used to declare a class in java.
3. public keyword is an access modifier which represents visibility, it means it is visible to all.
4. static is a keyword, if we declare any method as static, it is known as static method. The core advantage of static method is that there is no need to create object to invoke the static method. The main method is executed by the JVM, so it doesn't require to create object to invoke the main method. So it saves memory.
5. void is the return type of the method, it means it doesn't return any value.
6. main represents startup of the program.
7. String[] args is used for command line argument. We will learn it later.
8. System.out.println() is used print statement. We will learn about the internal working of System.out.println statement later.
5. Program Internal
In the previous page, we have learned about the first program, how to compile and how to run the first java program. Here, we are going to learn, what happens while compiling and running the java program. Moreover, we will see some question based on the first program.
What happens at compile time?
At compile time, java file is compiled by Java Compiler (It does not interact with OS) and converts the java code into bytecode.

What happens at runtime?
At runtime, following steps are performed:

Classloader: is the subsystem of JVM that is used to load class files.
Bytecode Verifier: checks the code fragments for illegal code that can violate access right to objects.
Interpreter: read bytecode stream then execute the instructions.
6. How to set path?
The path is required to be set for using tools such as javac, java etc.
If you are saving the java source file inside the jdk/bin directory, path is not required to be set because all the tools will be available in the current directory.
But If you are having your java file outside the jdk/bin folder, it is necessary to set path of JDK.
There are 2 ways to set java path:
temporary
permanent
1) How to set Temporary Path of JDK in Windows
To set the temporary path of JDK, you need to follow following steps:
Open command prompt
copy the path of jdk/bin directory
write in command prompt: set path=copied_path
For Example:
set path=C:\Program Files\Java\jdk1.6.0_23\bin
2) How to set Permanent Path of JDK in Windows
For setting the permanent path of JDK, you need to follow these steps:
Go to MyComputer properties -> advanced tab -> environment variables -> new tab of user variable -> write path in variable name -> write path of bin folder in variable value -> ok -> ok -> ok
For Example:
1)Go to MyComputer properties

2)click on advanced tab

3)click on environment variables

4)click on new tab of user variables

5)write path in variable name

6)Copy the path of bin folder

7)paste path of bin folder in variable value

8)click on ok button

9)click on ok button

Now your permanent path is set.You can now execute any program of java from any drive.
7. Difference between JDK,JRE and JVM
JVM
JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.
JVMs are available for many hardware and software platforms. JVM, JRE and JDK are platform dependent because configuration of each OS differs. But, Java is platform independent.
The JVM performs following main tasks:
· Loads code
· Verifies code
· Executes code
· Provides runtime environment
JRE
JRE is an acronym for Java Runtime Environment.It is used to provide runtime environment.It is the implementation of JVM.It physically exists.It contains set of libraries + other files that JVM uses at runtime.
Implementation of JVMs are also actively released by other companies besides Sun Micro Systems.

JDK
JDK is an acronym for Java Development Kit.It physically exists.It contains JRE + development tools.

8. Internal Details of JVM
JVM (Java Virtual Machine)
JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.
JVMs are available for many hardware and software platforms (i.e.JVM is plateform dependent).
What is JVM?
It is:
A specification where working of Java Virtual Machine is specified. But implementation provider is independent to choose the algorithm. Its implementation has been provided by Sun and other companies.
An implementation Its implementation is known as JRE (Java Runtime Environment).
Runtime Instance Whenever you write java command on the command prompt to run the java class, and instance of JVM is created.
What it does?
The JVM performs following operation:
1. Loads code
2. Verifies code
3. Executes code
4. Provides runtime environment
JVM provides definitions for the:
1. Memory area
2. Class file format
3. Register set
4. Garbage-collected heap
5. Fatal error reporting etc.
Internal Architecture of JVM
Let's understand the internal architecture of JVM. It contains classloader, memory area, execution engine etc.

1. Classloader:
Classloader is a subsystem of JVM that is used to load class files.
2. Class(Method) Area:
Class(Method) Area stores per-class structures such as the runtime constant pool, field and method data, the code for methods.
3. Heap:
It is the runtime data area in which objects are allocated.
4. Stack:
Java Stack stores frames.It holds local variables and partial results, and plays a part in method invocation and return.
Each thread has a private JVM stack, created at the same time as thread.
A new frame is created each time a method is invoked. A frame is destroyed when its method invocation completes.
5. Program Counter Register:
PC (program counter) register. It contains the address of the Java virtual machine instruction currently being executed.
6. Native Method Stack:
It contains all the native methods used in the application.
7. Execution Engine:
It contains:
1) A virtual processor
2) Interpreter:Read bytecode stream then execute the instructions.
3) Just-In-Time(JIT) compiler:It is used to improve the performance.JIT compiles parts of the byte code that have similar functionality at the same time, and hence reduces the amount of time needed for compilation.Here the term ?compiler? refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.
9. Variable and Data Type
Variable and Datatype in Java
In this page, we will learn about the variable and java data types. Variable is a name of memory location. There are three types of variables: local, instance and static. There are two types of datatypes in java, primitive and non-primitive.
Variable
Variable is name of reserved area allocated in memory.

int data=50;//Here data is variable
Types of Variable
There are three types of variables in java
· local variable
· instance variable
· static variable

Local Variable
A variable that is declared inside the method is called local variable.
Instance Variable
A variable that is declared inside the class but outside the method is called instance variable . It is not declared as static.
Static variable
A variable that is declared as static is called static variable. It cannot be local.
We will have detailed learning of these variables in next chapters.
Example to understand the types of variables
class A{
int data=50;//instance variable
static int m=100;//static variable
void method(){
int n=90;//local variable
}
}//end of class
Data Types in Java
In java, there are two types of data types
· primitive data types
· non-primitive data types

Data Type
Default Value
Default size
boolean
false
1 bit
char
'\u0000'
2 byte
byte
0
1 byte
short
0
2 byte
int
0
4 byte
long
0L
8 byte
float
0.0f
4 byte
double
0.0d
8 byte
Why char uses 2 byte in java and what is \u0000 ?
because java uses unicode system rather than ASCII code system. \u0000 is the lowest range of unicode system.
10. Unicode System
Unicode System
Unicode is a universal international standard character encoding that is capable of representing most of the world's written languages.
Why java uses Unicode System?
Before Unicode, there were many language standards:
· ASCII (American Standard Code for Information Interchange) for the United States.
· ISO 8859-1 for Western European Language.
· KOI-8 for Russian.
· GB18030 and BIG-5 for chinese, and so on.
This caused two problems:
1. A particular code value corresponds to different letters in the various language standards.
2. The encodings for languages with large character sets have variable length.Some common characters are encoded as single bytes, other require two or more byte.
To solve these problems, a new language standard was developed i.e. Unicode System.
In unicode, character holds 2 byte, so java also uses 2 byte for characters.
lowest value:\u0000
highest value:\uFFFF
11. Operators
Operators in java
Operator is a special symbol that is used to perform operations. There are many types of operators in java such as unary operator, arithmetic operator, relational operator, shift operator, bitwise operator, ternary operator and assignment operator.
Precedence of Operators
Operators
Precedence
postfix
expr++ expr--
unary
++expr --expr +expr -expr ~ !
multiplicative
* / %
additive
+ -
shift
<< >> >>>
relational
< > <= >= instanceof
equality
== !=
bitwise AND
&
bitwise exclusive OR
^
bitwise inclusive OR
|
logical AND
&&
logical OR
||
ternary
? :
assignment
= += -= *= /= %= &= ^= |= <<= >>= >>>=
Useful Programs:
There is given some useful programs such as factorial number, prime number, fibonacci series etc.
It is better for the freshers to skip this topic and come to it after OOPs concepts.
1) Program of factorial number.
class Operation{
static int fact(int number){
int f=1;
for(int i=1;i<=number;i++){
f=f*i;
}
return f;
}
public static void main(String args[]){
int result=fact(5);
System.out.println("Factorial of 5="+result);
}
}
2) Program of fibonacci series.
class Fabnoci{
public static void main(String...args)
{
int n=10,i,f0=1,f1=1,f2=0;
for(i=1;i<=n;i++)
{
f2=f0+f1;
f0=f1;
f1=f2;
f2=f0;
System.out.println(f2);
}
}
}
3) Program of armstrong number.
class ArmStrong{
public static void main(String...args)
{
int n=153,c=0,a,d;
d=n;
while(n>0)
{
a=n%10;
n=n/10;
c=c+(a*a*a);
}
if(d==c)
System.out.println("armstrong number");
else
System.out.println("it is not an armstrong number");
}
}
4) Program of checking palindrome number.
class Palindrome
{
public static void main( String...args)
{
int a=242;
int n=a,b=a,rev=0;
while(n>0)
{
a=n%10;
rev=rev*10+a;
n=n/10;
}
if(rev==b)
System.out.println("it is Palindrome");
else
System.out.println("it is not palinedrome");
}
}
5) Program of swapping two numbers without using third variable.
class SwapTwoNumbers{
public static void main(String args[]){
int a=40,b=5;
a=a*b;
b=a/b;
a=a/b;
System.out.println("a= "+a);
System.out.println("b= "+b);
}
}
6) Program of factorial number by recursion
class FactRecursion{
static int fact(int n){
if(n==1)
return 1;
return n*=fact(n-1);
}
public static void main(String args[]){
int f=fact(5);
System.out.println(f);
}
}
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