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Java Virtual Machine

A Java Virtual Machine (JVM) is a well-engineered software specifically created to help Java programs and applications  run on multiple platforms, operating systems and hardware.

Java Virtual Machine got this name because it provides a necessary virtual environment for Java Byte Code to execute. The flexibility of a JVM allows any Java program to be written only once, but it can be run on virtually any operating system or platform.

A Java Virtual Machine accepts standardized binary formatted code called Byte Code. Java compilers help translate the source code into the necessary format needed by the JVM. This organized approach ensures portability and stability of Java implementation on a wide array of hardware devices.

A JVM is usually bundled along with the Java Runtime Environment (JRE). JVM is a very important component of the Java platform.

Hotspot is the most widely used JVM presently. It is coded in C++ and developed by Oracle Corporation. Other companies can also make JVMs but they have to follow the JVM Specifications put down by Oracle.

A JVM runtime environment can execute two types of files – .class and .jar. It uses a special compiler called just-in-time to interpret the code.

Java applets run in a user’s web browser and provide functionality that cannot be performed by HTML, such as games, calculators, and chat applications. In order to run a Java applet, a Java plug-in must be installed and the JVM must be running. Java applets are considered very safe to run, even if they are unknown or untested, since they are essentially isolated from the rest of the computer’s functionality. This isolation technique is often referred to as the sandbox.

There is no shortage of support for Java and Java virtual machines. Large corporations such as Apple, IBM, and Hewlett-Packard develop closed-source (proprietary, thus not made public) Java virtual machine implementations. There is also a large amount of interest and support from the open-source development community for developing Java virtual machines. Open source simply means that the source code is available to anyone for free to further develop and improve upon.

Though Java is typically enabled by default on popular browsers such as Internet Explorer, due to the malicious intent of hackers and unscrupulous web marketers, some web surfers feel safer by disabling Java. This can eliminate some of the very annoying pop-under advertisements that exploit the Java permissions that are typically left to default settings. Java can typically be accomplished in the browser’s preferences menu.

Sun distributes the JVM as part of the JRE and also as part of the J2EE, J2SE, and J2ME.

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