Learning Java

The Java Compiler

In this section, we’ll say a few words about javac, the Java compiler that is supplied as part of Sun’s SDK. (If you are happily working in another development environment, you may want to skip ahead to the next section.) The javac compiler is written entirely in Java, so it’s available for any platform that supports the Java runtime system. The ability to support its own development environments is an important stage in a language’s development. Java makes this bootstrapping automatic by supplying a ready-to-run compiler at the same cost as porting the interpreter.

javac turns Java source code into a compiled class that contains Java virtual machine byte-code. By convention, source files are named with a .java extension; the resulting class files have a .class extension. Each source code file is a single compilation unit. As you’ll see in Chapter 6, classes in a given compilation unit share certain features, such as package and import statements.

javac allows you one public class per file and insists the file have the same name as the class. If the filename and class name don’t match, javac issues a compilation error. A single file can contain multiple classes, as long as only one of the classes is public. Avoid packing many classes into a single source file. Including non-public classes in a .java file is one easy way to tightly couple such classes to a public class. But you might also consider using inner classes (see Chapter 6).

Now for an example. Place ...