The document provides an overview of Java and its advantages. It discusses that Java is a platform-independent, object-oriented programming language that is simpler than C++ and enables writing of portable code via bytecode. It can be used to create both standalone applications and applets for web pages. The document also presents some history and key features of Java like robust memory management, security, and being well-suited for network-based applications.

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CORE-JAVA
By SimiBy Simi

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First, a bit of background…
 11stst
Generation – machine languageGeneration – machine language
 (raw machine code – lots of binary 0100101010001000111)
 22ndnd
Generation – assembly languageGeneration – assembly language
 (mnemonic representation – short series of chars to represent binary)
 33rdrd
Generation – structured programmingGeneration – structured programming
 (e.g. Pascal, C, C++, Java)
 44thth
Generation – application specificGeneration – application specific
 (SQL, Mathematica, RPG II, PostScript)
 55thth
Generation – combining artificial intelligenceGeneration – combining artificial intelligence
 (best not mentioned…)

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Towards Structured Programming
 As computer programs become largerAs computer programs become larger
and more complex, more errors areand more complex, more errors are
introduced.introduced.
 It has been estimated that there are 15It has been estimated that there are 15
bugs in every 1000 lines of commercialbugs in every 1000 lines of commercial
code.code.
 Windows 2000 had 40 million lines ofWindows 2000 had 40 million lines of
code!code!
 Most bugs are caused by poor memoryMost bugs are caused by poor memory
management.management.

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Contd:
 Clearly there is a need for a structuredClearly there is a need for a structured
programming language that helps inprogramming language that helps in
reducing the number of errors andreducing the number of errors and
speeds development for programmingspeeds development for programming
teams.teams.
 CC →→ C++C++ →→ JavaJava

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Contd:
 Functional ProgrammingFunctional Programming →→ ObjectObject
OrientationOrientation
““C makes it easy to shoot yourself in theC makes it easy to shoot yourself in the
foot; C++ makes it harder, but when itfoot; C++ makes it harder, but when it
happens you tend to take off the wholehappens you tend to take off the whole
leg!”leg!”

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What is Object-Oriented code?
 Procedural coding is just a list of instructions.Procedural coding is just a list of instructions.
 Object-oriented code has a lot of similarity withObject-oriented code has a lot of similarity with
code from other procedural languages.code from other procedural languages.
 Basically, a lot of the ‘words’ are the same but theBasically, a lot of the ‘words’ are the same but the
way the words are put together (the structure) isway the words are put together (the structure) is
different.different.

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Contd:
 Object-oriented coding does also contain lists ofObject-oriented coding does also contain lists of
instructions but these lists are bound to specificinstructions but these lists are bound to specific
objects.objects.
 What an object actually represents is up to theWhat an object actually represents is up to the
programmer.programmer.

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Simple Example
 AA car is an object (in the real world) and in ourcar is an object (in the real world) and in our
program we can make a software object toprogram we can make a software object to
represent it.represent it.
 Fundamentally, an object contains data andFundamentally, an object contains data and
methods which can act on that data.methods which can act on that data.
 The data we might want to have in our ‘software’The data we might want to have in our ‘software’
car could be things like: body colour, engine size,car could be things like: body colour, engine size,
current speed, whether it has electric windows etc.current speed, whether it has electric windows etc.
Basically it’s up to you.Basically it’s up to you.

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Simple Example
 The methods we might want our ‘car’ to haveThe methods we might want our ‘car’ to have
could be things like: accelerate, brake, respraycould be things like: accelerate, brake, respray
body, open passenger window etc. Again, it’s up tobody, open passenger window etc. Again, it’s up to
you.you.
 Whatever you need your software car to modelWhatever you need your software car to model
from the real world object must be present in yourfrom the real world object must be present in your
code.code.
 The OO syntax enables you to do this intuitively.The OO syntax enables you to do this intuitively.

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What technology does it replace?
 Procedural programming (C, Visual Basic, FortranProcedural programming (C, Visual Basic, Fortran
etc.)etc.)
 In procedural programming, functions were theIn procedural programming, functions were the
most important part of the software.most important part of the software.
 Where and how the data was stored was secondaryWhere and how the data was stored was secondary
(at best).(at best).
 Procedural code is process-oriented, OO code isProcedural code is process-oriented, OO code is
data-oriented.data-oriented.
 In procedural programming, if your code is in errorIn procedural programming, if your code is in error
then it is relatively easy to fix but incorrect datathen it is relatively easy to fix but incorrect data
may bemay be impossibleimpossible to fix!to fix!

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Java (why use it?)
Advantages over C & C++Advantages over C & C++
 WORA - Write Once, Run Anywhere (portable).WORA - Write Once, Run Anywhere (portable).
 Security (can run “untrusted” code safely).Security (can run “untrusted” code safely).
 Robust memory management (opaque references,Robust memory management (opaque references,
automatic garbage collection)automatic garbage collection)
 Network-centric programming.Network-centric programming.

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Java (why use it?)
 Multi-threaded (multiple simultaneous tasks).Multi-threaded (multiple simultaneous tasks).
 Dynamic & extensible.Dynamic & extensible.
 Classes stored in separate files
 Loaded only when needed
 Can dynamically extend itself to expand its
functionality (even over a network and the
Internet!)

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How does it help?
 Large projects can be broken down into modulesLarge projects can be broken down into modules
more easily.more easily.
 Aids understanding.Aids understanding.
 Groupwork is easier.Groupwork is easier.
 Less chance of data corruption.Less chance of data corruption.
 Aids reusability/extensibility.Aids reusability/extensibility.
 Maintaining code is far easier.Maintaining code is far easier.
 Hides implementation details (just need to knowHides implementation details (just need to know
what methods to call but no need to understandwhat methods to call but no need to understand
how the methods work to use them).how the methods work to use them).

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What is Java?
 Java (with a capital J) is a high-level, third
generation programming language, like C,
Fortran, Smalltalk, Perl, and many others.
 You can use Java to write computer applications
that crunch numbers, process words, play games,
store data or do any of the thousands of other
things computer software can do.

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Contd:
 Compared to other programming languages,
Java is most similar to C. However although
Java shares much of C's syntax, it is not C.
Knowing how to program in C or, better yet,
C++, will certainly help you to learn Java more
quickly, but you don't need to know C to learn
Java.
 Unlike C++ Java is not a superset of C.

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Contd:
 A Java compiler won't compile C code, and
most large C programs need to be changed
substantially before they can become Java
programs.
 What's most special about Java in relation to
other programming languages is that it lets you
write special programs called applets that can
be downloaded from the Internet and played
safely within a web browser.

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Applets
 embed into web page using applet tagembed into web page using applet tag
 <APPLET src = "myprogram.class" width =
"100" height = "100"> < /APPLET>
 source code extends Java Applet classsource code extends Java Applet class
 has skeleton user interfacehas skeleton user interface
 programmer can add code to be executedprogrammer can add code to be executed
when applet is initialised and paintedwhen applet is initialised and painted
 programmer can easily add GUI componentsprogrammer can easily add GUI components
such as buttons, labels, textfields, scrollbars….such as buttons, labels, textfields, scrollbars….
and respond to their eventsand respond to their events

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Java applications
 stand-alone programsstand-alone programs
 not GUI by defaultnot GUI by default
 text input and output to a console
 can add user interface components
 execution always starts at aexecution always starts at a main()main()
methodmethod

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Applets vs. applications
 Java appletsJava applets
 a program embedded into a web page
 download and run on user's browser
(or applet viewer)
 internet programming

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Applets vs. Applications
 Java applicationsJava applications
 stand-alone programs – Java is a
fully-fledged programming language
 many Java class libraries for
 GUI, graphics, networking
 data structures
 database connectivity
 we will be writing applications in thiswe will be writing applications in this
module.module.

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A Brief History
 January 1996: first official release JDK 1.0
 February 1997: JDK 1.1
 May 2000: J2SDK v1.3
 May 2001: J2SDK v1.4 beta
 2002(?): J2SDK v1.5

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Java is a Platform
 Java (with a capital J) is a platform for
application development.
 A platform is a loosely defined computer
industry buzzword that typically means
some combination of hardware and
system software that will mostly run all
the same software.

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Java is a Platform
 Java solves the problem of platform-
independence by using byte code. The Java
compiler does not produce native executable
code for a particular machine like a C compiler
would. Instead it produces a special format
called byte code. Java byte code written in
hexadecimal, byte by byte, looks like this:
CA FE BA BE 00 03 00 2D 00 3E 08 00 3B 08
00 01 08 00 20 08

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 This looks a lot like machine language,
but unlike machine language Java byte
code is exactly the same on every
platform. This byte code fragment
means the same thing on a Solaris
workstation as it does on a Macintosh
PowerBook.

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Java is a Platform
 Java programs that have been compiled
into byte code still need an interpreter to
execute them on any given platform.
 The interpreter reads the byte code and
translates it into the native language of
the host machine.
 The most common such interpreter is
Sun's program java (with a little j)

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Java is a Platform
 Since the byte code is completely platform
independent, only the interpreter and a few
native libraries need to be ported to get Java to
run on a new computer or operating system.
 The rest of the runtime environment including
the compiler and most of the class libraries are
written in Java. All these pieces, the javac
compiler, the java interpreter, the Java
programming language, and more are
collectively referred to as Java.

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Java is Simple
 Java is an excellent teaching language,
and an excellent choice with which to
learn programming.
 The language is small so it's easy to
become fluent. The language is
interpreted so the compile-run-link cycle
is much shorter.

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Java is Platform Independent
 Java was designed to not only be cross-
platform in source form like C, but also in
compiled binary form.
 Since this is frankly impossible across
processor architectures Java is compiled to an
intermediate form called byte-code.
 A Java program never really executes natively
on the host machine. Rather a special native
program called the Java interpreter reads the
byte code and executes the corresponding
native machine instructions.

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Java is Platform Independent
 Thus to port Java programs to a new platform
all that is needed is to port the interpreter and
some of the library routines.
 Even the compiler is written in Java. The byte
codes are precisely defined, and remain the
same on all platforms.

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Java is Platform Independent
 The second important part of making Java
cross-platform is the elimination of undefined
or architecture dependent constructs.
Integers are always four bytes long, and
floating point variables follow the IEEE 754
standard for computer arithmetic exactly.
 You don't have to worry that the meaning of
an integer is going to change if you move from
a Pentium to a PowerPC.
 In Java everything is guaranteed.

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Java is High Performance
 Java byte codes can be compiled on the fly to
code that rivals C++ in speed using a "just-in-
time compiler.“
 Several companies are also working on native-
machine-architecture compilers for Java.
 These will produce executable code that does
not require a separate interpreter, and that is
indistinguishable in speed from C++.

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Java is Multi-Threaded
 Java is inherently multi-threaded. A
single Java program can have many
different threads executing
independently and continuously.
 Three Java applets on the same page
can run together with each getting equal
time from the CPU with very little extra
effort on the part of the programmer.

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Java is Dynamic(ly linked)
 Java does not have an explicit link phase. Java
source code is divided into .java files, roughly
one per each class in your program.
 The compiler compiles these into .class files
containing byte code. Each .java file generally
produces exactly one .class file.

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Java is Dynamic(ly linked)
 The compiler searches the current directory
and directories specified in the CLASSPATH
environment variable to find other classes
explicitly referenced by name in each source
code file. If the file you're compiling depends
on other, non-compiled files the compiler will
try to find them and compile them as well.

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Java is Garbage Collected
 You do not need to explicitly allocate or
deallocate memory in Java.
 Memory is allocated as needed, both on the
stack and the heap, and reclaimed by the
garbage collector when it is no longer needed.
 There's no malloc(), free(), or destructor
methods.

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Characteristics of Java
• Simple
• Object-oriented
• Compiled
• Architecture neutral
• Garbage collected
• Multi-threaded
• Robust
• Secure
• Extensible

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Packages
• Java provides mechanisms to organize large-
scale programs in a logical and maintainable
fashion.
 – Class --- highly cohesive functionalities
 – File --- one class or more closely related
classes
 – Package --- a collection of related classes or
packages

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A simple Java application
class HelloJava
{
public static void main (String args[])
{
System.out.println("Hello Java!");
}
}

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Writing Java code
 When you've chosen your text editor, type or
copy the above program into a new file.
 Like C and unlike Fortran, Java is case sensitive
so System.out.println is not the same as
system.out.println. CLASS is not the same as
class, and so on.
 there are three steps to creating a Java
program:
 – writing the code
 – compiling the code
 – running the code

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First Java Program
 Under Windows, it's similar. You just do
this in a DOS shell.
C:> javac HelloWorld.java
C:> java HelloWorld
Hello World
 C:>
• Notice that you use the .java extension
when compiling a file, but you do not
use the .class extension when running a
file.

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First Java Program
 Under Windows (98 and before) you set the
CLASSPATH environment variable with a DOS
command like
 C:> SET
CLASSPATH=C:JDKJAVACLASSES;c:javalib
classes.zip
For Newer Windows platforms (including
Windows XP), type the following-
C:> set path=C:j2sdk1.4.0-rcbin
And press ENTER
 (where j2sdk1.4.0 is the folder in your root
(C:>) drive, where Java2SDK is installed)

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First Java Program
 The CLASSPATH variable is also
important when you run Java applets,
not just when you compile them. It tells
the web browser or applet viewer where
it should look to find the referenced
.class files.
 If the CLASSPATH is set improperly,
you'll probably see messages like
"Applet could not start."

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 If the CLASSPATH environment variable
has not been set, and you do not specify
one on the command line, then Java
sets the CLASSPATH to the default.

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The class and its method in
JAVA
 name of class is same as name of filename of class is same as name of file
(which has(which has ..java extension)java extension)
 body of class surrounded by { }body of class surrounded by { }
 this class has one method called mainthis class has one method called main
 all Java applications must have a main
method in one of the classes
 execution starts here
 body of method within { }
 all other statements end with semicolon;all other statements end with semicolon;

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Java keywords
 keywords appear in boldkeywords appear in bold
 reserved by Java for predefined
purpose
 don’t use them for your own variable,
attribute or method names!
 publicpublic
 visibility could be private

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Java keywords
 voidvoid
 method does not return a value
 staticstatic
 the main method belongs to the Hello
class, and not an instance (object) of
the class.

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Comments
 important for documentation!!!!important for documentation!!!!
 ignored by compilerignored by compiler
//// single line (or part of line)single line (or part of line)
/* multiple line comments go here/* multiple line comments go here
everything between the markseverything between the marks
is ignored */is ignored */

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THANK YOUTHANK YOU