Java Reference
In-Depth Information
Chapter 2. Interacting with the
Environment
Introduction
This chapter describes how your Java program can deal with its immediate surroundings,
with what we call the runtime environment. In one sense, everything you do in a Java pro-
gram using almost any Java API involves the environment. Here we focus more narrowly on
things that directly surround your program. Along the way we'll be introduced to the
System
class, which knows a lot about your particular system.
Two other runtime classes deserve brief mention. The first,
java.lang.Runtime
, lies behind
many of the methods in the
System
class.
System.exit()
, for example, just calls
Runtime.exit()
.
Runtime
is technically part of “the environment,” but the only time we
use it directly is to run other programs, which is covered in
Running an External Program
Getting Environment Variables
Problem
You want to get the value of “environment variables” from within your Java program.
Solution
Use
System.getenv()
.
Discussion
The seventh edition of Unix, released in 1979, had a new feature known as environment vari-
ables. Environment variables are in all modern Unix systems (including Mac OS X) and in
