This document provides an overview of Java and its key features. It discusses how Java was created to be platform independent and allow code to run on any system. The document introduces the Java Virtual Machine (JVM) which allows Java bytecode to run on any platform. It describes some of Java's main features like being object-oriented, robust, secure, and architecturally neutral. The document also compares Java to C++ and discusses some limitations of Java. Example Java code is provided to demonstrate a simple class and method definitions.

1. Advance Java Lab
1
By
Vishal Choudhary
Department of Computer Engineering, PCE

2. 2

4. With the invention of internet and world
wide web there is need of a language that
should be platform independent.
On internet we don't know in advance at
what platform our code or program
/application will be executed as all over the
world there are heterogeneous systems.

5. JAVA was not made for Internet
programming. Java was developed for
Microcontroller for platform neutral
execution. so there is no need to rewrite the
code each time for every Microcontroller.

6. James Gosling and his team start working on
a portable ,platform independent language
that could be used to produce code that
would run on variety of CPU under different
environment.
This effort leads to creation of JAVA

7. In portable language we can compile the
code by using different compiler on different
operating system.
e.g. in C source code
 On DOS we can compile the source code by
Turbo Borland Compiler
 On Window we can compile using VC++
Compiler
 For UNIX we can use CC/GCC compiler

8. JAVA VIRTUAL MACHINE is the
solution for platform independent
compilation

9. Specification designed by SUN Microsystems
1. Instruction set
2. File format
3. Class loading and execution Mechanism etc.
JVM is specification of JRE
JRE is implementation of JVM
JRE can be called JVM but JVM cannot be called JRE.
Car is called a Vehicle but Vehicle is not called Car

10.  A software vendor who wants to develop JRE
needs JVM
Main component of JRE
1 Byte code verifier
2.Class Loader
3.Just in time Compiler
4.Class Library
5.Security Policies
6.Memory Management.

11.  It is the package of JRE and tools(javac ,javap ,jar
etc.)
(jar is compression and decompression format of sun micro
system)
1. Application programmer needs JDK
2. End user needs JRE
3. A software vendor who wants to develop JRE
needs JVM(specification and license from
SunMicrosystem now owned by Oracle).
4. Every vendor can develop their own compiler of
java with license from sun micro system
according to their need.

12. The key to solve the security and portability
problem is that the output of Java compiler is not
executable code rather than it is BYTECODE.
Byte Code is a highly optimized set of
instructions to be executed by JRE(some time
called JVM)
JVM was designed as an interpreter for byte code.
JVM may be different from platform to platform
but all understand the same byte code.

13.  In real world we think in the form of object. We
give preference to object than on work that object
perform.
e.g: Teacher, Carpenter
JAVA designer want to develop a language that
should solve the problems that have solution
similar real world problems.
If we want to study we looks for teacher.
If we want to make a table, chair or any furniture we
looks for carpenter

14.  Object is an Instance of class
 At particular moment how that class is
behaving is know as object
 Suppose Light is class
Either it is on ,off,dim,bright
Light is on
Light is off
Light is bright
Light is Dim

17.  it is the way of thinking in terms of object on
the basis of this thinking a programming
model created by sun micro system in known
as object oriented programming structure
 SUN MicroSystem is a microelectronics
company designing chips for microcontroller
used in washing machines ,digital set top
box,Remote control etc.
 What is difference between microcontroller
and microprocessor?

18. Java's main features are
 1. Platform independent.
 2. Security

19.  For each platform we have to write a new
code.
 If a company is making 100 microcontroller
per day then 100 times we have to write the
code. because language depends on the
properties of hardware(instruction set,
instruction format, type of register)

20. Main Feature of Java:
1. Simple
2. Secure(The JVM performs verification on bytecode before running it to prevent the program
from performing unsafe operations such as branching to incorrect locations)
3. Object-Oriented
4. Robust(Java is robust because it is highly supported language, meaning that
unlike C you cannot crash your computer with a bad program)
5. Multithreaded
6. Architectural Neutral
(binary code format" that's independent of hardware
architectures, operating system interfaces, and window
systems)
7. Interpreted.
8. High-performance
(Just in time compilation)
9. Distributed (development of application to run over network
always need distributed languages)
10. Dynamic (During the execution of a program, Java can
dynamically load class libraries )

21.  It is slow in comparison of C/C++.because it
is both compiled and interpreted language.
 Applet cannot access local data. Only
download the data from site where applet is
located.
 No use of pointer so we cannot do flexible
data structure design.
 Need different JVM for different platform.
 It is strictly types language (every variable
have type, every expression has type) so
there is no flexibility in programming.

22. JAVA C++
1 Java is completely object oriented
language
C++ is extension of C with object oriented
behavior
2 Java does not support multiple
inheritances. But it can be achieved
using interface if needed.
C++ support multiple inheritance
3 Java does not support global
variable
Global variable can be declared in C++
4 Java does not support pointer. C++ support pointers.
5 In Java there is no destructor. In C++ there is use of destructor
6 Java does not provide header file C++ has header file.
7 Java code run on Virtual machine
(JVM)
C++ code runs on actual machine
8 In java automatic memory
management and garbage collection
Memory management is done manually by
new/delete.
9 Write once run any where Write once compile anywhere

30. Class MyExample
{
public Static Void main(String arr[])
{
System.out.println(“this is my example”);
}
}

31.  The word Class means that a new class is defined.
 MyExample is an identifier(called class name)
 All members of class should be declared inside
curly braces {…………….}
 Execution always start from main method.
 The keyword public mean that member may be
accessed by code outside the class in which it is
declared.
 main() must be declared as public since it must be
called by the code outside of its class when the
program is started.
 Keyword static allow main() to be called without
having to instantiate a particular instance of class.
since main() is called by JVM before any object are
made.

32.  Keyword void tells the compiler that main()
does not return a value.
 Object of type String store character string in
this case arr is an command line argument
presents when program is executed.
 System is a predefined class that provides
access to the system and out is output
stream that is connected to console.

33. Execution Model of C and C++
1.Application file is read and format is checked.
2.If format is valid .its instruction is loaded.
3.Address of first Inst. Is loaded in PC
4.Process asked to start execution.
5.Address of Instruction fetched from PC one by one.
6.Instruction is fetched from memory and is executed.

34. 2.Class file is read and its format is checked.
3,4.If format is valid, class loader is asked to load it.
5.Just in time compiler(JITC) is asked to execute the class.
6.Instruction of class is read one by one.
7.For each instruction security policy is checked and instruction is
executed only if it satisfy security policy.

35.  .
 Eclipse

36. Class Rectangle
{
int l,b
//attribute
public void display()
{
System.out.println(“Length=”+l);
System.out.println(“Breadth=”+b);
}
public int area()
{
Return l*b;
}
Public void setDimension(int x,int y)
{
I=x;
B=y;
}
}
Class RectangleTest
{
public static void main(String
arr[])
{
Rectangle r = new Rectangle();
r.setDimension(20,30)
{
System.out.println(“dimension of
rectangle are”);
r.display();
System.out.println(“area of
rectangle r is =”+r.area());
}}

37.  Classname refrencevariable = new classname();
 Reference variable is a implicit pointer which
is used to contain the reference of objects.
 In java reference variable are dynamically
created. Hence they don’t have name and are
referenced through their reference variables.
 In C++: there is static allocation of objects
 r
 Rectangle r ======== r
l
b