System Properties
Problem
You need to get information from the system properties.
Solution
Use System.getProperty( )
or System.getProperties( ).
Discussion
What is a property anyway? A property is just a name and value pair
stored in a java.util.Properties object, which
we’ll discuss more fully in Section 7.8. So if
I chose to, I could store the following properties in a
Properties object called ian:
name=Ian Darwin favorite_popsicle=cherry favorite_rock group=Fleetwood Mac favorite_programming_language=Java pencil color=green
The Properties
class has several forms of its retrieval
method. You could, for example, say
ian.getProperty("pencil
color")
and get back the string “green”. You can also provide a
default: say ian.getProperty("pencil color", "black"), and if the property has not been set you would
get the default value “black”.
For now, we’re concerned with the
System
class
and its role as keeper of the particular
Properties object that controls and describes the
Java runtime. The System class has a static
Properties member whose content is the merger of
operating system specifics
(os.name, for example), system and user tailoring
(java.class.path), and properties defined on the
command line (as we’ll see in a moment). Note that the use of
periods in these names (like os.arch,
os.version and java.class.path,
java.lang.version) makes it look as though there
is a hierarchical relationship similar to that for class names. The
Properties class, however, imposes no such relationships: ...