[Chapter 14] System Properties

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| Chapter 14 |

# 14. System Properties

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()`.

## 14.1 Standard System Properties

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.)

Table 14.1: Standard System 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

Java Documentation Comment Syntax |  | Working with System Properties