Java fundamentals

Instructor: @Subash @Paudyal
Pokhara & Tribhuvan University
Kathmandu, Nepal
Training on Java
Programming

• Java Introduction
• Java History
• Why Learn Java
• Java Version
• Java IDE
• Java Features
• Java Program Structure
• What happens at Compile and Runtime ?
• Distinction between JVM, JRE and JDK
Session 1: Fundamentals
© paudyalsubash@yahoo.com 2

• Java is a programming language and a platform.
• Java is a high level, robust, secured and object-oriented
programming language.
Introduction (What java)

• James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language
project in June 1991.
• Firstly, it was called "Greentalk" by James Gosling and file extension was .gt.
• After that, it was called Oak and was developed as a part of the Green project.
• Why Oak? Oak is a symbol of strength and chosen as a national tree of many
countries like U.S.A., France, Germany, Romania etc. (presumably because he liked
the look of an oak tree that was right outside his window at Sun).
• In 1995, Oak was renamed as "Java" because it was already a trademark by Oak
Technologies.
• Why java? The team gathered to choose a new name. 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.
• Java is an island of Indonesia where first coffee was produced (called java coffee).
• Originally developed by James Gosling at Sun Microsystems (which is now a
subsidiary of Oracle Corporation) and released in 1995.
History (How Java)

Why Java?
• Large codebase of already written applications
• 9 million of professional Java developers
• Lots of enterprise applications were developed and are being
developed in Java
• The same program can run on different platforms
• Mobile Android development is done in Java
• According to Sun, 3 billion devices run java. There are many
devices where java is currently used.

• Some of the devices using java 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.
Devices using Java

• There are mainly 4 type of applications that can be created using java
programming:
• Standalone Application: (J2SE) – Standard Edition
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.
• 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.
• Enterprise Application: (J2EE) – Enterprise Edition
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.
• Mobile Application: (J2ME) – Micro Edition
An application that is created for mobile devices. Currently Android and Java ME are used for
creating mobile applications.
Types of Java Applications

• Simple
• Object oriented
• Platform independent
• Secured
• Multi-threaded
• Robust
• Portable
• High Performance
Features of Java

• 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.
Simple

• 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
Object Oriented

• 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:
• Runtime Environment
• API(Application Programming Interface)
• java is platform independent 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).
Platform Independent

• Java is secured because:
• No explicit pointer
• Programs run inside virtual machine sandbox.
• Security provided by Java Language
• Classloader
• adds security by separating the package for the classes of
the local file system from those that are imported from
network sources.
• Bytecode Verifier
• checks the code fragments for illegal code that can violate
access right to objects.
• Security Manager
• determines what resources a class can access such as
reading and writing to the local disk.
Secure

• 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.
• 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.
• We may carry the java bytecode to any platform.
• Java is faster than traditional interpretation since byte code is "close"
to native code still somewhat slower than a compiled language (e.g.,
C++)
Multi-Tasking, Robust, Portable, high
performance

Run First Program
• Three steps to run the Java
program
 Write the program and save it in a file
with the name that ends with .java,
for example
HelloWorld.java
 Compile the program using javac
compiler which creates
HelloWorld.class file, for example
javac HelloWorld.java
 Run your program:
java HelloWorld
class HelloWorld {
public static void main(String[] args)
{
System.out.println (“Hello,
world!");
}
}

• class keyword is used to declare a class in java.
• public keyword is an access modifier which represents visibility, it means it is visible to all.
• (if its not public JVM classes might not able to access it)
• 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.
• (While JVM tries to execute Java program it doesn't know how to create instance of main
class as there is no standard constructor is defined for main class)
• void is the return type of the method, it means it doesn't return any value.
• (because it doesn't return any thing to caller which is JVM)
• main represents startup of the program.
• String[] args is used for command line argument. We will learn it later.
• System.out.println() is used print statement. We will learn about the internal working of
System.out.println statement later.
Understanding Keywords

• At compile time, java file is compiled by Java Compiler and
converts the java code into bytecode.
• It does not interact with OS
What happens at compile time?

What happens at runtime?

• 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
Difference between JVM, JRE and JDK

• 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.
JRE

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

Java IDE
• Integrated Development Environment (IDE)
• Makes your work more productive
• Includes text editor, compiler, debugger, context sensitive, help,
works with different Java SDKs
• Most widely used IDEs:
• Netbeans (Oracle)
• Eclipse (Open)
• Intellijidea (Jetbrains)

• Queries?
End of Java Introduction

Java fundamentals

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