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 program 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 meet 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.exit( ) , for example, just calls
Runtime.exit( ) . It is technically part of “the environment,” but the
only time we use it directly is to run other programs, which is covered
in Recipe 26.1. The
java.awt.Toolkit object is also part
of the environment and is discussed in Chapter 13.
You want to get the value of "environment variables” from within your Java program.
Don’t (JDK 1.4 and earlier). Go ahead, but be careful (JDK 1.5).
The seventh edition of Unix, released in 1979, had an exciting new feature known as environment variables. Environment variables are in all modern Unix systems (including Mac OS X) and in most later command-line systems, such as the DOS subsystem underlying Windows, but are not in some older platforms or other Java runtimes. Environment variables are commonly used for customizing an individual computer user’s runtime ...