Java

Table of Content

• Overview
• History
• Modules
• Appendix

Overview

• Java is one of the world’s most important and widely used computer languages.

• Java is loaded with lots of features like Open Source, Simple, Secure, Portable, Object Oriented, Multithreaded, Interpreted and Distributed.

• Java Basic Terminologies

  • JCP: The Java Community Process is the process that formalizes and standardizes Java technologies.
  • JSR: The Java Specification Requests is used to introduce new technologies into the language. Not all JSR specifications are taken up by the language.
  • JDK: The Java Development Kit is a complete Java development platform with JavaCompiler, JavaDocs and JavaDebugger
  • JRE: The Java Runtime Environment provides an environment where Java applications can run effectively.
  • JVM: The Java Virtual Machine (JVM) is responsible for supporting the execution of Java applications.
  • JCL: The Java Class Library is a set of standard libraries that is available to any application running on the JVM.
  • Java EE: The Java Enterprise Edition (Java EE) was created to extend the Java SE by adding a set of specifications that define capabilities commonly used by enterprise applications.

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History

• History of Java programming language is usually associated with origin predates of the web. Below is the evolution of Java
  • In 1991, The Green Project at Sun Micro Systems(now Oracle) begins looking for a purpose. They take apart many electronic devices, like cable TV set-top boxes and remote controls to find a way for the appliances to talk to each other.
  • The Green Project (Naughton, Gosling and Sheridan) settles on smart consumer electronics as the delivery platform. Gosling starts development of a new programming language and by August 1991, James Gosling at Sun created a language C++ ++. His friends asked to name it something else and then he called it as Oka (on the name of tree found outside his window).
  • By October 1992, 7 inch a cross between a PDA and a remote control, is ready. This is demoed to Scott McNealy who is blown away. Following that demo, the Green Project is set up as First Person Inc, a wholly owned Sun subsidiary.
  • In early 1993, The Green Project hears about a Time-Warner request for proposal for a setup box operating system. First Person Inc quickly shifts focus from smart consumer electronics (which is proving to be more hype than reality) to the setup box OS market, and place a bid with Time-Warner. They lose the bid.
  • In early 1994, First Person Inc concludes that like smart consumer electronics setup boxes were more hype than reality. Without a market to be seen First Person is rolled back into Sun.
  • After failing at interactive media, people at Sun sat together in a coffee shop to figure out what they have to do with Oak and decided rename it to Java by Gosling after looking at the menu.
  • In 1994, a team of Java developers started writing Web Runner, which was a clone of the internet browser Mosaic. It was based on the Java programming language. The name Web Runner was a tribute to the Blade Runner movie. Web Runner's first public demonstration was given by John Gage and James Gosling at the Technology Entertainment Design Conference in Monterey, California in 1995. It was later renamed Hot Java, it was officially announced in May the same year at the Sun World conference.
  • Hot Java was a modular, extensible web browser from Sun Microsystems implemented in Java. It was the first browser to support Java applets, and was Sun's demonstration platform for the then-new technology.

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Architecture

• System hardware interacts with executable software using Operating System (OS). OS is responsible for allocation and de-allocation of resource based on request from different software programs.

• A Virtual Machine is a software implementation of a physical machine inside OS. Java was developed with the concept of WORA (Write Once Run Anywhere), which runs on a VM.

• The heart of Java programing language is JVM. The compiler compiles the Java file into a .class file and then that .class file is inputted into the JVM to load and executes the class file.

• Below is the detailed overview of JVM Architecture

  

  • Class Loader Sub System:
    • This is used to load, link and initialize a class file when JVM refers to a class for the first time.
      • Loading
        • The class loader sub system reads the .class file and generate corresponding binary data in method area.
        • There are three types of class loaders
          • Bootstrap/Primordial Class Loader
            • It is responsible to load core Java API classes (jdk/jre/lib/rt.jar)
            • This is implemented in native languages like C, C++ and not in Java.
          • Extension Class Loader
            • Loads the classes available in the extension class path (jdk/jre/lib/ext)
            • This is implemented in Java.
          • Application/System Class Loader
            • Loads the classes available in the class path.
            • This is implemented in Java.
      • Linking
        • This process involves the below:
          • Verification:
            • Check if metadata of class file is structurally correct.
            • JVM will check if class file is generated on a valid compiler using Byte Code Verifier.
          • Preparation:
            • In this phase static variables will be initialized with default values.
          • Resolution:
            • This will replace symbolic names of java program with memory location references from method area.
      • Initialization
        • This will initialized static variables with actual assignment values and execute static blocks if defined
        • The execution is from top to bottom and parent to child.
    • This process kicks during runtime and not in compile time.
    • Sub System used Delegation Algorithm to load a class.
      • When a new class file is asked to be loaded then system will check if class is loaded. If not loaded then it will ask class sub system to load the class.
      • Class loader sub system handovers the request of loading to Application -> Extension -> Bootstrap.
      • If class is not available in Bootstrap it delegates request to Extension and then to Application.
      • If class is not available in any loader then system will raise ClassNotFoundException
      • Classes loaded in child will be visible in the parent i.e. classes loaded in Application are visible in Extension and Bootstrap.

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Installation

• Download the latest version of java based on your operating system architecture from Oracle jdk .

• Execute the Installer and please select the installation folder.

  

• Continue with the installation for the subsequent steps.

  

  

• Setting of Path for Java

  • Right-click on 'My Computer' and select 'Properties'.

  • Click on the 'Environment variables' button under the 'Advanced' tab.

  • Alter the 'Path' variable so that it also contains the path to the Java executable

    • In the case of our example ( See second point ) the java executable lies at C:\Program Files\Java\jdk1.8.0_221\bin

  • Confirm the installation by checking the java version in the command prompt

    java -version

    

  • Creating a First program in Java.

    • Create a file name 'HelloWorld.java' using a Text editor
    • Write the Below code in it.

        public class HelloWorld {
          public static void main(String[] args) throws Exception {
              System.out.println("Hello Java");
          }
        }

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Modules

• This program details most important module of Core Java features:
  • OOPS Concepts
  • Data Types, Variables, and Arrays
  • Operators
  • Control Statements
  • Class & Object
  • Packages and Interfaces
  • Exception Handling
  • Annotations
  • Generics
  • Collections Framework
  • I/O Operations & NIO
  • Concurrency Utilities
  • Regular Expressions
  • Lambda Expressions
  • Date & Time Functions
• Advanced concepts of
  • JUnit
  • Logging
  • Servlet
  • JAXB
  • Jackson
  • Bean Validation
  • CDI
  • Universal Connection Pooling
  • JPA
  • Jax-RS
  • Reactive Programing

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Appendix

• References
  • Java 8 Complete Reference