Difference between JDK, JRE and JVM

 More Important and Fluently Asked In Interview

JVM

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

How to set path in Java

The path is required to be set for using tools such as javac, java etc.

If you are saving the java source file inside the jdk/bin directory, path is not required to be set because all the tools will be available in the current directory.
But If you are having your java file outside the jdk/bin folder, it is necessary to set path of JDK.

There are 2 ways to set java path:

1. temporary
2. permanent

1) How to set Temporary Path of JDK in Windows

To set the temporary path of JDK, you need to follow following steps:

• Open command prompt
• copy the path of jdk/bin directory
• write in command prompt: set path=copied_path

For Example:

set path=C:\Program Files\Java\jdk1.6.0_23\bin

2) How to set Permanent Path of JDK in Windows

For setting the permanent path of JDK, you need to follow these steps:

• Go to MyComputer properties -> advanced tab -> environment variables -> new tab of user variable -> write path in variable name -> write path of bin folder in variable value -> ok -> ok -> ok

 

 

Simple Program of Java

By : Mungara Chirantan

In this page we will learn How to Start A first Java program and how we can Run it . ok so lets Start

To create a simple java program, you need to create a class that contains main method. Let's understand the requirement first.

Requirement for Java Program Development 

• install the JDK if you don't have installed it, download the JDK and install it.
• set path of the jdk/bin directory.
• create the java program
• compile and run the java program

Creating hello java example

 Class XYZ

{

    public Static void main(String args[]);

 {

      System.out.println("Hello Gays How are U");

} }

Note :

1. save this file as a class name like XYZ.java.
2. compile : javac xyz.java
3. execute  : java xyz.java

Understanding first java program

• 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.
• 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.
• void is the return type of the method, it means it doesn't return any value.
• 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.

Valid java main method signature

1. public static void main(String[] args)  
2. public static void main(String []args)  
3. public static void main(String args[])  
4. public static void main(String... args)  
5. static public void main(String[] args)  
6. public static final void main(String[] args)  
7. final public static void main(String[] args)  
8. final strictfp public static void main(String[] args) 

 Invalid java main method signature

 

1. public void main(String[] args)  
2. static void main(String[] args)  
3. public void static main(String[] args)  
4. abstract public static void main(String[] args) 

Features of Java

By : Chirantan Mungara

Here is given many feature of java and also java feature also none as Buzzwords all features is given bellow :

1. Simple
2. Object-Oriented
3. Platform independent
4. Secured
5. Robust
6. Architecture neutral
7. Portable
8. Dynamic
9. Interpreted
10. High Performance
11. Multithreaded
12. Distribute

• Simple

  1) Simple means java  Syntax is base on C++ so easy to learn after c++.
  2) and also remove many confusing and/or rarely use feature like explicit pointer and operator overloading.
  3) and also in java no need to remove unreferenced variable because java have Automatic Garbage collector
   

• Object-oriented

  object oriented means we organise our software as a combination of different type of object that is incorporate both data and behaviour.
  
  
  Class
  Object
  Inheritance
  Polimorphisam
  Abstraction
  Encapsulation
   

• Platform Independent

  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 code can be run on multiple platforms

• Secured

   

   Java is secured because:
  
  
  • No explicit pointer
  • Programs run inside virtual machine sandbox.

   

  Robust

  • 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. 
  
  

  Architecture-neutral

  • There is no implementation dependent features e.g. size of primitive types is set. 
  
  

  Portable

  • We may carry the java bytecode to any platform. 

  High-performance

  • Java is faster than traditional interpretation since byte code is "close" to native code still somewhat slower than a compiled language (e.g., C++) 

  Distributed

  • We can create distributed applications in java. RMI and EJB are used for creating distributed applications. We may access files by calling the methods from any machine on the internet. 

  Multi-threaded

  • 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. 

History of Java

By : Mungara Chirantan

Java history is interesting to know And very Easy To Unserstand. The history of java starts from Green Team. Java team members (also known as Green Team), initiated a revolutionary task to develop a language for digital devices such as set-top boxes, televisions and many more .

For the green team members, it was an advance concept at that time. But, it was

suited for internet programming. Later, Java technology as incorporated by Netscape.

Currently lava use many platform like internet programming, mobile devices, games, e-business solutions etc

There are given the major points



1) James Gosling, Mike Sheridan, and PatrickNaughton initiated the Java language project in June 1991. The small team of sun engineers called Green Team .

James Gosling

 2) Originally designed for small, embedded systems in electronic appliances like set-top boxes.

3) Firstly, it was called "Greentalk" by James Gosling and file extension was .gt.

4) After that, it was called Oak and was developed as a part of the Green project.

Why Oak name for java language?

 

5) Why Oak? Oak is a symbol of strength and choosen as a national tree of many countries like U.S.A., France, Germany, India etc.

6) In 1995, Oak was renamed as "Java" because it was already a trademark by Oak Technologies.

 

Why Java name for java language?

Resign is : 

Why they choosed java name for java language? 

The team gathered to choose a new name. The suggested words were "dynamic", "revolutionary", "Silk", "jolt", "DNA" etc. They wanted something that reflected the essence of the technology: revolutionary, dynamic, lively, cool, unique, and easy to spell and fun to say look like interesting.

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 And suggested by James Gosling.

Java is an island of Indonesia where first coffee was produced (called java coffee).

 Notice that Java is just a name not an acronym.

 Originally developed by James Gosling at Sun Microsystems (which is now a subsidiary of Oracle Corporation) and released in 1995.

In 1995, Time magazine called Java one of the Ten Best Products of 1995.

 JDK 1.0 released in(January 23, 1996).

Java Version History ?

As given bellow :-

1. JDK Alpha and Beta (1995)
2. JDK 1.0 (23rd Jan, 1996)
3. JDK 1.1 (19th Feb, 1997)
4. J2SE 1.2 (8th Dec, 1998)
5. J2SE 1.3 (8th May, 2000)
6. J2SE 1.4 (6th Feb, 2002)
7. J2SE 5.0 (30th Sep, 2004)
8. Java SE 6 (11th Dec, 2006)
9. Java SE 7 (28th July, 2011)
10. Java SE 8 (18th March, 2014)

What Is Java? & Where it is use? & Which type of Application we design in Java ?

This type of several Question Are comes to over mind when we Fresher

1 : What Is Java ?

Ans :

         java is a programming Language and Platform Independence Language

(But here generate one more question what is Platform Independence : Ans Is : Any Hardware and Software Environment in which our program is run That is call Platform Independence )

2 : where it is use ?

Ans :

         According to Sun More then 3 billion Application Are Run in java Platform

1. Desktop Applications such as acrobat reader, media player, anti-virus etc
2. Web Applications such as irctc.co.in
3. Enterprise Applications such as banking applications.
4. Mobile
5. Embedded System
6. Smart Card
7. Robotics
8. Games etc.

3 : Type of Java Applications we Design in Java

 

1) Standalone Application

       It is also none as Desktop Application or Windows base Application . an application we need to install each and every PC. like Anti-virus , Media Player etc

2) Enterprise Application

      An application distribute in nature like banking application. It has advantages is High level Security  load balancing and clustering. In java, EJB is used for creating enterprise applications.

3) 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.

4) Mobile Application

An application that is created for mobile devices. Currently Android and Java ME are used for creating mobile applications.

 

                Thanks For Read My Tutorial

                       Mungara Chirantan