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Chapter 14 |  |
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Chapter 14 | |
Contents:
Standard System Properties
Working with System Properties
Java programs cannot read environment variables the way that native programs can. The reason is that environment variables are platform dependent. Similar mechanisms exist, however, that allow applications to read the value of a named resource. These resource values allow customization of an application's behavior based on site-specific parameters, such as the type of host, or based on user preferences.
These named resource values are specified for applications in the "system properties" list. Applications can read these "system properties" with the System.getProperty() method, or can read the entire list of properties with System.getProperties(). System.getProperty() returns the property value as a string. Applications can also read properties in parsed form using methods that are based on System.getProperty(), such as Font.getFont(), Color.getColor(), Integer.getInteger(), and Boolean.getBoolean().
When the Java interpreter starts, it inserts a number of standard properties into the system properties list. These properties, and the meaning of their values, are listed in Table 14.1. The table also specifies whether untrusted applets are allowed (at least by default) to read the value of these properties. For reasons of security, untrusted code is only allowed to read the values of properties to which it has explicitly been granted access. (Untrusted applets are not allowed to set the value of system properties, nor are they allowed to call System.getProperties() to obtain the entire list of properties.)
| Name | Value | Applet Access |
|---|---|---|
| java.version | Version of the Java interpreter | yes |
| java.vendor | Vendor-specific identifier string | yes |
| java.vendor.url | Vendor's URL | yes |
| java.class.version | The version of the Java API | yes |
| java.class.path | The classpath value | no |
| java.home | The directory Java is installed in | no |
| java.compiler |
The JIT compiler to use, if any (Java 1.1) |
no |
| os.name | The name of the operating system | yes |
| os.arch | The host hardware architecture | yes |
| os.version | Version of the host operating system | yes |
| file.separator |
Platform-dependent file separator (e.g., / or #) |
yes |
| path.separator |
Platform-dependent path separator (e.g., : or ;) |
yes |
| line.separator |
Platform-dependent line separator (e.g., #n or #r#n) |
yes |
| user.name | The username of the current user | no |
| user.home | The home directory of the current user | no |
| user.dir | The current working directory | no |
| user.language |
The 2-letter language code of the default locale (Java 1.1) |
no |
| user.region |
The 2-letter country code of the default locale (Java 1.1) |
no |
| user.timezone | The default time zone (Java 1.1) | no |
| file.encoding |
The character encoding for the default locale (Java 1.1) |
no |
| file.encoding.pkg |
The package that contains converters between local encodings and Unicode (Java 1.1) |
no |
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| Java Documentation Comment Syntax |  |
Working with System Properties |
