The JavaTM Tutorial

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Trail: Essential Java Classes
Lesson: Accessing System Resources

## The Runtime Object

> At the core of the Java runtime environment are the Java virtual machine, the Java interpreter, and the host operating system.

> The oval labelled Runtime in the diagram represents the current runtime environment and is an instance of the `Runtime` class. The current runtime environment could be anything from Sun's implementation of the Java virtual machine and interpreter running on Solaris to ACME Company's implementation of the virtual machine and interpreter running on the ACME toaster.

> `Runtime` objects provide two services. First, they communicate with the components of the runtime environment--getting information and invoking functions. Second, `Runtime` objects are also the interface to system-dependent capabilities. For example, UNIX `Runtime` objects might support the `getenv` and `setenv` functions. Other `Runtime` objects, such as for Mac OS, might not support `getenv` and `setenv` because the host operating system doesn't support these functions, but they might support others.

> Because the `Runtime` class is tightly integrated with the implementation of the Java interpreter, the Java virtual machine, and the host operating system, it is system-dependent. If objects in your program message the `Runtime` object directly, you sacrifice the system indepedent nature of your Java program. In general, this is not a good idea (particularly for applets).

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