Introduction of JAVA

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Introduction of Java

A team of 5 members of Sun Microsystems Inc. - James Gosling, Patrick Naughton, Chris Warth, Ed Frank and Mike Sheridan developed a programming language named OAK in 1991 to program for an electronic devices (Home Appliances). “Oak” was renamed as Java in 1995. Java is a 3rd Generation OOP language as well as a leader for Internet Programming.

 

Type of Java Programs

1. Application Program

A Stand Alone program that runs as a true application without a browser using JVM is known as Application Program which usually contains a main function.

2. Applet Program

A Java program that can be included in an HTML page which can be executed on a web browser. It uses a java.applet package to add small interactive components to a webpage.

Translator

The computer understands only Machine Language. So the programs written in any programming language (High-Level Language or Object-Oriented Language) must be translated into a Machine Language, so that the computer can understand an execute it.

 

Translation Process in High-Level Languages:

Source Program in HLL (Source Code)

à

Compiler (All at Once)

à

Machine Language (Machine Code) or (Object Code)

OR

Source Program in HLL (Source Code)

à

Interpreter (Line by Line)

à

Machine Language (Machine Code) or (Object Code)

 

Java Program Translation Process:

Java uses two translators

1.    Java Compiler

2.    Java Interpreter

 

Java Source Program

à

Java Compiler (javac)

à

Java Byte Code

à

Java Interpreter (java JVM

à

Machine Language

 

Source Code .java file

(Native Code) .class file

(Machine Code) or (Object Code)

 

 

Java program is first translated by Java Compiler which converts the given Source Code into Java Byte Code. The Java Byte Code is a Native Code which is a common for all types of machines irrespective of the hardware or software used in a machine. In next step, Java Interpreter (JVM) will translate the Java Byte Code into Machine Language which can be executed on end-user computer.

i.e. Java programs using a compiler (javac) for converting Java source code (.java files) to Java bytecode (.class files). Once this is done, Java Virtual Machine (JVM) loads the .class files at run time and converts them to a machine understandable code using an interpreter.

Java is a Platform-Independent Language which means the program written in a Java Language can be executed on any kind of platform irrespective of the hardware or software used in a machine without any changes in Java program. It also known as WORA (Write Once Run Anywhere).

Java Development Kit (JDK) is a bundle of software components that is used to develop Java based applications includes JRE, and the compilers and tools (like JavaDoc, and Java Debugger) to create and compile programs.

JRE is an acronym for Java Runtime Environment. It is an implementation of the Java Virtual machine, which actually executes Java programs. It includes the JVM (Java Virtual machine), core libraries and other additional components to run applications and applets written in Java.

The JDK is a superset of the JRE, and contains everything that is in the JRE, plus tools such as the compilers and debuggers necessary for developing applets and applications. It also includes browser plugins for Applet execution. The JRE does not contain tools and utilities such as compilers or debuggers for developing applets and applications.

Usually, when you only care about running Java programs on your browser or computer you will only install JRE. That's all you need. On the other hand, if you are planning to do some Java development, you will also need JDK.

Features of Java:

1. Simple Coding

2. Robust – Java provides a automatic memory management and a garbage collection along with strong exception handling (checking & handling for errors) mechanism that makes it robust.

3. Secured – it support many in-built security that makes the system secure from crash.

4. Object Oriented – It support OOPs concepts.

5. Platform Independent

6. WORA - Write Once Run Anywhere

Object Oriented Programming Concept or Principles of OOPs:

1. Object - An identifiable entity with two characteristics – State and Behavior is known as Object. A State represents the properties of an object and Behavior represents What task an object can do. An Object is an Instance of a Class. It contains all the Instance Variables which is defined in a same class as a non-static variable.

 

2. Class - Class is a blueprint or template for an Object. Class works as an Object Factory. A class defines the State and Behavior of an Object. A class is a collection of Data and Methods together as a single unit. Class is also used to create a new User Defined Data type which contains similar or non-similar type of values. i.e. A class is used to create a new data type which can contains a different type of values. It also known as Composite Data Type.

 

3. Encapsulation - The process of wrapping up of Data & its associated functions which work on the same data is known as Encapsulation. To implement the concept of Encapsulation, a class is used.

 

4. Data Abstraction - It specifies that the necessary things will be available for use without knowing the background things like how it is working. It is implemented using private and protected access specifier in Java. It actually hides the data from being accessible in other classes.

 

5. Polymorphism - Polymorphism is the concept where an object behaves differently in different situations. There are two types of polymorphism:

Compile-Time Polymorphism (Early Binding or Static Binding or Linking) Implemented through Function Overloading, Constructor Overloading & Operator Overloading & Linking is done at Compile-Time.

Run-Time Polymorphism (Late Binding or Dynamic Binding or Linking) Where Linking is done at Run-Time.

Runtime polymorphism is implemented when we have “IS-A” relationship between objects. This is also called as method overriding because subclass has to override the super class method for runtime polymorphism.

 

6. Inheritance - Reusability is yet another aspect of OOP paradigm. It is always nice if we could reuse something that already exists rather than creating the same all over again. Java classes can be reused in several ways. This is basically done by creating new classes, reusing the properties of existing ones. The mechanism of deriving a new class from an old one is called Inheritance. The old class is known as the base class or super class or parent class and the new one is called the subclass or derived class or child class.

Inheritance is implemented using a keyword extends for a class and a keyword implements for an Interface in Java.

 

The inheritance allows subclasses to inherit all the variables and methods of their parent classes.

Inheritance may take different forms:

1.    Single inheritance (only one super class)

2.    Multiple inheritance (several super classes)

3.    Hierarchical inheritance (one super class, many subclasses)

4.    Multilevel inheritance (Derived from a derived class)

5.    Hybrid inheritance