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Trail: Writing Applets
Lesson: Practical Considerations when Writing Applets

## Getting System Properties

> To find out about the current working environment, applets can read system properties. System properties are key/value pairs that contain information such as the operating system that the applet is running under. System properties are covered in detail in the System Properties page.

> Applets can read some, but not all, system properties. This page lists the system properties that Netscape Navigator 2.0 and the Applet Viewer allow applets to read, followed by a list of properties that applets can't read.

### System Properties that Applets Can Read

> Applets can read the following system properties:

> Key | Meaning
> `"file.separator"` | File separator (for example, "/")
> `"java.class.version"` | Java class version number
> `"java.vendor"` | Java vendor-specific string
> `"java.vendor.url"` | Java vendor URL
> `"java.version"` | Java version number
> `"line.separator"` | Line separator
> `"os.arch"` | Operating system architecture
> `"os.name"` | Operating system name
> `"path.separator"` | Path separator (for example, ":")

> To read a system property from within an applet, the applet uses the `System` class method `getProperty`. For example:

> >     String newline = System.getProperty("line.separator");

> The following applet reads all of the properties that are available to all applets:

> You can find the source code (which is the same in both 1.0 and 1.1) in `GetOpenProperties.java`.

### Forbidden System Properties

> For security reasons, no existing browsers or applet viewers let applets read the following system properties.

> Key | Meaning
> `"java.class.path"` | Java classpath
> `"java.home"` | Java installation directory
> `"user.dir"` | User's current working directory
> `"user.home"` | User home directory
> `"user.name"` | User account name

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