The Java Technology Phenomenon

Java technology seems to be everywhere, but what exactly is it? The following sections explain how Java technology is both a programming language and a platform, and provide an overview of what this technology can do for you.

About the Java Technology

Java technology is both a programming language and a platform. The Java Programming Language is a high-level language that can be characterized by all of the following buzzwords: Simple, Object oriented Distributed, Multithreaded, Dynamic, Architecture neutral, Portable, High performance, Robust, Secure.

An overview of the software development process.

Because the Java VM is available on many different operating systems, the same .class files are capable of running on Microsoft Windows, the Solaris™ Operating System (Solaris OS), Linux, or Mac OS. Some virtual machines, such as the Java SE Hotspot at a Glance, perform additional steps at runtime to give your application a performance boost. This includes various tasks such as finding performance bottlenecks and recompiling (to native code) frequently used sections of code. Through the Java VM, the same application is capable of running on multiple platforms.

The Java Platform

A platform is the hardware or software environment in which a program runs. We've already mentioned some of the most popular platforms like Microsoft Windows, Linux, Solaris OS, and Mac OS. Most platforms can be described as a combination of the operating system and underlying hardware. The Java platform differs from most other platforms in that it's a software-only platform that runs on top of other hardware-based platforms. The Java platform has two components:

  • The Java Virtual Machine
  • The Java Application Programming Interface (API)

You've already been introduced to the Java Virtual Machine; it's the base for the Java platform and is ported onto various hardware-based platforms. The API is a large collection of ready-made software components that provide many useful capabilities. It is grouped into libraries of related classes and interfaces; these libraries are known as packages. Highlights some of the functionality provided by the API.

The API and Java Virtual Machine insulate the program from the underlying hardware. As a platform-independent environment, the Java platform can be a bit slower than native code. However, advances in compiler and virtual machine technologies are bringing performance close to that of native code without threatening portability. The terms "Java Virtual Machine" and "JVM" mean a Virtual Machine for the Java platform.

What Can Java Technology Do?

The general-purpose, high-level Java programming language is a powerful software platform. Every full implementation of the Java platform gives you the following features:

  • Development Tools: The development tools provide everything you'll need for compiling, running, monitoring, debugging, and documenting your applications. As a new developer, the main tools you'll be using are the javac compiler, the java launcher, and the javadoc documentation tool.
  • Application Programming Interface (API): The API provides the core functionality of the Java programming language. It offers a wide array of useful classes ready for use in your own applications. It spans everything from basic objects, to networking and security, to XML generation and database access, and more. The core API is very large; to get an overview of what it contains, consult the Java Platform Standard Edition 7 Documentation.
  • Deployment Technologies: The JDK software provides standard mechanisms such as the Java Web Start software and Java Plug-In software for deploying your applications to end users.
  • User Interface Toolkits: The JavaFX, Swing, and Java 2D toolkits make it possible to create sophisticated Graphical User Interfaces (GUIs).
  • Integration Libraries: Integration libraries such as the Java IDL API, JDBC API, Java Naming and Directory Interface (JNDI) API, Java RMI, and Java Remote Method Invocation over Internet Inter-ORB Protocol Technology (Java RMI-IIOP Technology) enable database access and manipulation of remote objects.
Java Features - Simple
  • Looks familiar to existing programmers: related to C and C++:
  • Omits many rarely used, poorly understood, confusing features of C++, like operator overloading, multiple inheritance, automatic coercions, etc.
  • Contains no goto statement, but break and continue
  • Has no header files and eliminated C preprocessor
  • Eliminates much redundancy (e.g. no structs, unions, or functions)
  • has no pointers
  • Added features to simplify:
  • Garbage collection, so the programmer won't have to worry about storage management, which leads to fewer bugs.
  • A rich predefined class library

Java is an object-oriented language, which means that you focus on the data in your application and methods that manipulate that data, rather than thinking strictly in terms of procedures. In an object-oriented system, a class is a collection of data and methods that operate on that data. Taken together, the data and methods describe the state and behaviour of an object. Classes are arranged in a hierarchy, so that a subclass can inherit behaviour from its superclass. Java comes with an extensive set of classes, arranged in packages that you can use in your programs. Distributed it has a spring-like transparent RPC system

  • Now uses mostly tcp-ip based protocols like ftp & http
  • Java supports various levels of network connectivity through classes in the package (e.g. the URL class allows a Java application to open and access remote objects on the internet).
  • Interpreted
  • The Java compiler generates byte-codes, rather than native machine code. To actually run a Java program, you use the Java interpreter to execute the compiled byte-codes. Java byte-codes provide an architecture-neutral object file format. The code is designed to transport programs efficiently to multiple platforms.
  • rapid turn-around development
  • Software author is protected, since binary byte streams are downloaded and not the source code
  • Robust
  • Java has been designed for writing highly reliable or robust software:
  • language restrictions (e.g. no pointer arithmetic and real arrays) to make it impossible for applications to smash memory (e.g overwriting memory and corrupting data)
  • Java does automatic garbage collection, which prevents memory leaks
  • extensive compile-time checking so bugs can be found early; this is repeated at runtime for flexibilty and to check consistency

Security is an important concern, since Java is meant to be used in networked environments. Without some assurance of security, you certainly wouldn't want to download an applet from a random site on the net and let it run on your computer. Java's memory allocation model is one of its main defences against malicious code (e.g. can't cast integers to pointers, so can't forge access). Furthermore:

  • Access restrictions are enforced (public, private)
  • Byte codes are verified, which copes with the threat of a hostile compiler
  • Architecture-Neutral
  • Compiler generates bytecodes, which have nothing to do with a particular computer architecture
  • Easy to interpret on any machine
  • Portable
  • Java goes further than just being architecture-neutral:
  • No "implementation dependent" notes in the spec (arithmetic and evaluation order)
  • Standard libraries hide system differences
  • The Java environment itself is also portable: the portability boundary is POSIX compliant

Java is an interpreted language, so it will never be as fast as a compiled language as C or C++. In fact, it is about 20 times as slow as C. However, this speed is more than enough to run interactive, GUI and network-based applications, where the application is often idle, waiting for the user to do something, or waiting for data from the network.


Java allows multiple concurrent threads of execution to be active at once. This means that you could be listening to an audio clip while scrolling the page and in the background downloading an image. Java contains sophisticated synchronization primitives (monitors and condition variables), that are integrated into the language to make them easy to use and robust. The java.lang package provides a Thread class that supports methods to start, run, and stop a thread, and check on its status.


Java was designed to adapt to an evolving environment:

  • Even after binaries have been released, they can adapt to a changing environment
  • Java loads in classes as they are needed, even from across the network
  • It defers many decisions (like object layout) to runtime, which solves many of the version problems that C++ has
  • Dynamic linking is the only kind there is