Introduction to java

Course Contents:

1. Introduction
2. History and development of java
3. Platform independence
4. Byte code
5. Object-oriented characteristics
6. How to write and execute?

History and development of Java

Year	Development
1990	Sun Microsystems decided to develop special software that could used to manipulate consumer electronic devices.
1991	After exploring the possibility of using the most popular object-oriented language C++, the team of Sun Microsystems announced a new language “OAK”.
1992	They use their new language to control a list of home appliances using hand held devices with a tiny touch sensitive screen.
1993	The team came up with idea of developing web applets (tiny programs) using the new language that could run on all types of computers connected to internet.
1994	The team developed a web browser called “HotJava” to locate and run applet program on internet. This becomes the most popular among the internet users.
1995	Oak was renamed “Java”. Java is just a name not an acronym and many popular companies like Netscape and Microsoft also support this language.

Platform Independence

If the software/program written in particular languages for a particular platform run in any other platform without changing the program, then we can say such types of programming language as platform independence i.e. run on any platform without changing the original program.

Java programs can be easily moved from one computer system to another, anywhere and anytime. Changes in the operating systems, processors and system resources will not force any changes in java program. So the java is the platform independent language.

Due to its independence nature java becomes popular language for programming on internet which interconnects different kinds of systems worldwide. Java becomes platform independent due to its two properties:

- Java compiler generates bytecode that can be implemented on any machine.

- The size of primitive data types are machine independent.

Bytecode

When the program written in java is compiled, the compiler generates an intermediate code instead of directly to platform specific machine code. This intermediate code is known as bytecode and is machine independent. This byte code is then translated to machine code by a interpreter known as Java virtual machine which is incorporated with every operating system.

Characteristics of Object-Oriented language

• Emphasis is on data rather than procedures.
• Programs are divided into objects.
• Data structures are designed such that they characterize the objects.
• Functions & data are tied together in the data structures so that data abstraction is introduced in addition to procedural abstraction.
• Data is hidden & can’t be accessed by external functions.
• Object can communicate with each other through f unction.
• New data & functions can be easily added.
• Follows Bottom up approach.

Features of Object Oriented Language:

1.Objects

Objects are the entities in an object oriented system through which we perceive the world around us. We naturally see our environment as being composed of things which

have recognizable identities & behavior. The entities are then represented as objects in the program. They may represent a person, a place, a bank account, or any item that the

program must handle. For example, Automobiles are objects as they have size, weight, color etc. as attributes (i.e. data) and starting, pressing the brake, turning the wheel, pressing accelerator pedal etc. as operation (that is functions).

Objects mainly serve the following purposes:

• Understanding the real world and a practical base for designers
• Decomposition of a problem into objects depends on the nature of problem.

2. Classes

A class is a collection of objects of similar type. For example, manager, peon, secretary, clerk are member of the class employee and class vehicle includes objects car, bus, etc.

It defines a data type, much like a struct in C programming language and built in data type(int char, float etc). It specifies what data and functions will be included in objects of that class. Defining class doesn’t create an object but class is the description of objects attributes and behaviors.

Person Class : Attributes: Name, Age, Sex etc.

Behaviors: Speak(), Listen(), Walk()

Vehicle Class: Attributes: Name, model, color, height etc

Behaviors: Start(), Stop(), Accelerate() etc.

When class is defined, objects are created as

<classname> <objectname> ;

If employee has been def ined as a class, then the statement

employee manager; Will create an object manager belonging to the class employee.

Each class describes a possibly infinite set of individual objects; each object is said to be an instance of its class and each instance of the class has its own value for each attribute but shares the attribute name and operations with other instances of the class. The following point gives the idea of class:

• A class is a template that unites data and operations.
• A class is an abstraction of the real world entities with similar properties.
• Ideally, the class is an implementation of abstract data type.

3. Encapsulation and Data Abstraction

The wrapping up of data and function into a single unit is called encapsulation. Encapsulation is most striking feature of a class. The data is not accessible from outside of class. Only member function can access data on that class. The insulation of data from direct access by the program is called data hiding. That is data can be hidden making them private so that it is safe from accidental alteration.

Abstraction is representing essential features of an object without including the background details or explanation. It focuses the outside view of an object, separating its essential behavior from its implementation.

The class is a construct in C++ for creating user-defined data types called Abstract Data Types (ADT).

4. Inheritance:

Inheritance is the process by which objects of one class acquire the characteristics of object of another class. In OOP, the concept of inheritance provides the idea of reusability. We can use additional features to an existing class without modifying it. This is possible by deriving a new class (derived class) from the existing one (base class). This process of deriving a new class from the existing base class is called inheritance.

It supports the concept of hierarchical classification. It allows the extension and reuse of existing code without having to rewrite the code.

5.Polymorphism

Polymorphism means “having many forms”. The polymorphism allows different objects to respond to the same message in different ways, the response specific to the type of object.

Polymorphism is important when object oriented programs dynamically creating and destroying the objects in runtime. Example of polymorphism in OOP is operator overloading, function overloading.

For example, operator symbol „+ is used for arithmetic operation between two numbers, however by overloading (means given additional job) same operator „+ can be used for different purpose like concatenation of strings.

Dynamic Biding

Binding refers to the linking a function call to the code to be executed in response to the call.

Dynamic binding means that the code associated with a given function call is not known until the time of the call at run time. It is associated with polymorphism & inheritance.

6.Message Passing

An Object-Oriented program consists of set of objects that communicate with each other. Object communicates with each other by sending and receiving message (information).

A message for an object is a request for execution of a procedure and therefore will invoke a function or procedure in receiving object that generate the desired result. Message passing involves specifying the name of the object name of the function (message) and the information to be sent.

How to write and execute java program

The following steps are involved during writing and executing java program.

1. Write a java program on any java editor or notepad
2. Save it inside the folder bin which is located at this path C:\Program Files\Java\jdk1.6.0\bin\
3. The name of the file must be same as the class name with extension .java

Procedure for compiling and running the java program

1. Open command mode
2. Set command mode path as C:\Program Files\Java\jdk1.6.0\bin\
3. Type <javac>space<filename.java> in command mode to compile the java program.
4. If there exist any error, compiler generates errors and removes that error. This process continues till the program becomes error free.
5. If the program is error fr ee then in compilation phase the compiler generates the intermediate code of the original source code with extension <filename.class>. Which is known as bytecode?
6. Then run the program with command <java>space<filename>.
7. Then you can see the required output.