Java Basic.pdf

Java Basic.pdf

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  Java Basic What isJava 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.
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  Portable − Beingarchitecture-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.
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  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
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  Development Kit isprovided 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.
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  3)Enterprise Application An applicationthat 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 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?
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  Explain how Javaprograms 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?