What is Java Java is a programming language and a platform. Java is a high level, robust, object-oriented and secure programming language. It was originally developed by Sun Microsystems which was initiated by James Gosling and released in 1995 as core component of Sun Microsystems' Java platform (Java 1.0 [J2SE]). The latest release of the Java Standard Edition is Java SE 10. With the advancement of Java and its widespread popularity, multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise Applications, J2ME for Mobile Applications. The new J2 versions were renamed as Java SE, Java EE, and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere. Exception in Java An exception is an unwanted or unexpected event, which occurs during the execution of a program i.e at run time, that disrupts the normal flow of the program’s instructions. Exception is an abnormal condition.In Java, an exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime. What is Spring Spring is a lightweight framework and an open source Java platform that provides comprehensive infrastructure support for developing robust Java applications very easily and very rapidly. Spring framework was initially written by Rod Johnson and was first released under the Apache 2.0 license in June 2003. This tutorial has been written based on Spring Framework version 4.1.6 released in Mar 2015. It can be thought of as a framework of frameworks because it provides support to various frameworks such as Struts, Hibernate, Tapestry, EJB, JSF, etc. The framework, in broader sense, can be defined as a structure where we find solution of the various technical problems. The Spring framework comprises several modules such as IOC, AOP, DAO, Context, ORM, WEB MVC etc. We will learn these modules in next page. Let's understand the IOC and Dependency Injection first. Web Service A web service is any piece of software that makes itself available over the internet and uses a standardized XML messaging system. XML is used to encode all communications to a web service. For example, a client invokes a web service by sending an XML message, then waits for a corresponding XML response. As all communication is in XML, web services are not tied to any one operating system or programming language java can talk with Perl; Windows applications can talk with Unix applications. Web Services tutorial is designed for beginners and professionals providing basic and advanced concepts of web services such as protocols, SOAP, RESTful, java web service implementation, JAX-WS and JAX-RS tutorials and examples. Web service is a technology to communicate one programming language with another. For example, java programming language can interact with PHP and .Net by using web services. In other words, web service provides a way to achieve interoperability. Web services are self-contained, modular, and distributed.

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What is JDK
Describe the key steps in
which a Java class is
loaded by the JVM?
What are runtime data
areas?
How is a java program
executed by JVM?
Explain how Java programs
are executed by the JVM?
What is the Java
bytecodes?
What is the difference
between JVM, JRE and
JDK?
How is Java programming
language machine and
platform independent?
What is Java
Java is a programming language and a platform. Java is a high level, robust, object-oriented and secure programming
language. It was originally developed by Sun Microsystems which was initiated by James Gosling and released in 1995 as
core component of Sun Microsystems' Java platform (Java 1.0 [J2SE]).
The latest release of the Java Standard Edition is Java SE 10. With the advancement of Java and its widespread
popularity, multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise
Applications, J2ME for Mobile Applications.
The new J2 versions were renamed as Java SE, Java EE, and Java ME respectively. Java is guaranteed to be Write
Once, Run Anywhere.
Features of Java
Object Oriented − In Java, everything is an Object. Java can be easily extended since it is based on the Object model.
Platform Independent − Unlike many other programming languages including C and C++, when Java is compiled, it is not
compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the
web and interpreted by the Virtual Machine (JVM) on whichever platform it is being run on.
Simple − Java is designed to be easy to learn. If you understand the basic concept of OOP Java, it would be easy to
master.
Secure − With Java's secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are
based on public-key encryption.
Architecture-neutral − Java compiler generates an architecture-neutral object file format, which makes the compiled code
executable on many processors, with the presence of Java runtime system.
Portable − Being architecture-neutral and having no implementation dependent aspects of the specification makes Java
portable. Compiler in Java is written in ANSI C with a clean portability boundary, which is a POSIX subset.
Robust − Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking
and runtime checking.
Multithreaded − With Java's multithreaded feature it is possible to write programs that can perform many tasks
simultaneously. This design feature allows the developers to construct interactive applications that can run smoothly.
Interpreted − Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The
development process is more rapid and analytical since the linking is an incremental and light-weight process.
High Performance − With the use of Just-In-Time compilers, Java enables high performance.
Distributed − Java is designed for the distributed environment of the internet.
Dynamic − Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving
environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve
accesses to objects on run-time.
History of Java
The history of Java is very interesting. Java was originally designed for interactive television, but it was too advanced
technology for the digital cable television industry at the time. The history of Java starts with the Green Team. Java team
members (also known as Green Team), initiated this project to develop a language for digital devices such as set-top
boxes, televisions, etc. However, it was suited for internet programming. Later, Java technology was incorporated by
Netscape.
The principles for creating Java programming were "Simple, Robust, Portable, Platform-independent, Secured, High
Performance, Multithreaded, Architecture Neutral, Object-Oriented, Interpreted, and Dynamic". Java was developed by
James Gosling, who is known as the father of Java, in 1995. James Gosling and his team members started the project in
the early '90s.
1) James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. The small team
of sun engineers called Green Team.
2) Initially designed for small, embedded systems in electronic appliances like set-top boxes.
3) Firstly, it was called "Greentalk" by James Gosling, and the file extension was .gt.
4) After that, it was called Oak and was developed as a part of the Green project.
Components
JVM (Java Virtual Machine)
It is an abstract machine. It is a specification that provides a run-time environment in which the bytecode can be
executed. It follows three notations:
Specification: It is a document that describes the implementation of the JVM. It is provided by Sun and other companies.
Implementation: It is a program that meets the requirements of JVM specification. Runtime Instance: An instance of JVM
is created whenever you write a command on the command prompt and run the class.
JRE (Java Runtime Environment) JRE refers to a runtime environment in which bytecode can be executed. It implements
the JVM and provides all the class libraries and other support files that JVM uses at runtime. So JRE is a software
package that contains what is required to run a program. Basically, it’s an implementation of the JVM which physically
exists.
JDK(Java Development Kit) It is the tool necessary to:- Compile Document Package Java programs. The JDK completely
includes JRE which contains tools for programmers. The Development Kit is provided free of charge. Along with JRE, it
includes an interpreter/loader, a compiler (javac), an archiver (jar), a documentation generator and other tools needed in
Java development. In short, it contains JRE + development tools.
Why Use Java?
Java works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.)
It is one of the most popular programming language in the world
It is easy to learn and simple to use
It is open-source and free
It is secure, fast and powerful
It has a huge community support (tens of millions of developers)
Java is an object oriented language which gives a clear structure to programs and allows code to be reused, lowering
development costs
As Java is close to C++ and C#, it makes it easy for programmers to switch to Java or vice versa
Types of Java Applications
There are mainly 4 types of applications that can be created using Java programming:
1) Standalone Application
Standalone applications are also known as desktop applications or window-based applications. These are traditional
software that we need to install on every machine. Examples of standalone application are Media player, antivirus, etc.
AWT and Swing are used in Java for creating standalone applications.
2) Web Application
An application that runs on the server side and creates a dynamic page is called a web application. Currently, Servlet,
JSP, Struts, Spring, Hibernate, JSF, etc. technologies are used for creating web applications in Java.
3) Enterprise Application
An application that is distributed in nature, such as banking applications, etc. is called enterprise application. It has
advantages of the high-level security, load balancing, and clustering. In Java, EJB is used for creating enterprise
applications.
4) Mobile Application
An application which is created for mobile devices is called a mobile application. Currently, Android and Java ME are used
for creating mobile applications.
What is Object-oriented?
Object-oriented programming (OOPs) is a methodology that simplifies software development and maintenance by
providing some rules. Java is an object-oriented programming language. Everything in Java is an object. Object-oriented
means we organize our software as a combination of different types of objects that incorporates both data and behavior.
Basic concepts of OOPs are:
Object
Class
Inheritance
Polymorphism
Abstraction
Encapsulation
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