Introduction to Java and Internet Applications

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1. Introduction to Java and Internet Applications

1.1 Overview of the Internet

  • Definition: The Internet is a global network of interconnected computers that communicate through standardized protocols to share information and resources.
  • History:
    • Developed from the ARPANET project initiated by the U.S. Department of Defense in the 1960s.
    • Public access grew in the late 1980s and early 1990s, leading to the Internet's widespread adoption.
  • Key Components:
    • Servers and Clients: Servers store and manage data, while clients request and display it.
    • IP Addresses: Unique numerical labels assigned to each device connected to the Internet.
    • Protocols: TCP/IP (Transmission Control Protocol/Internet Protocol) governs data transmission across the network.
    • World Wide Web: A collection of web pages accessible via the Internet using web browsers.

1.2 Java as a Tool for Internet Applications

  • Platform Independence:
    • Java's "write once, run anywhere" philosophy allows Java applications to run on any device that has a Java Virtual Machine (JVM).
    • This is particularly beneficial for web applications, where the same Java code can be executed on different platforms without modification.
  • Security Features:
    • Java has built-in security features such as a robust exception-handling mechanism, a secure class loading system, and a bytecode verifier that enhances security in web applications.
    • Applets, small Java programs embedded in web pages, run in a secure environment called the "sandbox," preventing unauthorized access to the system.
  • Applets and Servlets:
    • Applets: Java programs that can be embedded in HTML pages and run in web browsers, enabling dynamic and interactive content on web pages.
    • Servlets: Java programs that run on web servers and handle client requests, commonly used for generating dynamic content on websites.
  • Java's Popularity for Web Development:
    • Widely used for developing server-side applications, web services, and dynamic web content.
    • Frameworks like JavaServer Pages (JSP) and Spring further extend Java's capabilities in building robust web applications.

1.3 Understanding Byte Code

  • Definition: Bytecode is an intermediate code generated after the Java source code is compiled. It is a set of instructions that the JVM executes.
  • Compilation Process:
    • Java source code is written in .java files.
    • The Java compiler (javac) converts the source code into bytecode, which is stored in .class files.
    • Bytecode is platform-independent, meaning it can be executed on any device with a JVM.
  • Execution Process:
    • The JVM reads the bytecode and translates it into machine code specific to the host operating system.
    • This process, called Just-In-Time (JIT) compilation, occurs at runtime, allowing Java applications to run efficiently on various platforms.

1.4 Advantages of Byte Code

  • Platform Independence:
    • Bytecode enables Java applications to run on any platform with a JVM, eliminating the need for platform-specific code.
  • Security:
    • Bytecode is verified by the JVM for security before execution, preventing malicious code from running.
  • Portability:
    • The same bytecode can be distributed across different systems, ensuring that the application behaves consistently regardless of the underlying hardware or operating system.
  • Optimization:
    • JVMs can optimize bytecode during runtime for better performance, adapting to the specific hardware it runs on.