'javac' - The Java Compiler

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This chapter describes:

• "javac" Command
• Hello.class - My First Class File
• "-classpath" - Specifying Class Path
• "-sourcepath" - Specifying Source Path
• "-d" - Specifying Output Directory
• "import" Statements
• "-g" Controlling Debugging Information

"javac" Command

"javac": A command line tool that reads Java source files and compiles them into bytecode class files. "javac" is distributed as part of the Sun JDK package. It has the following syntax:

javac [options] [sourcefiles]

where "options" is a list of options and "sourcefiles" is a list of Java source files.

Commonly used options are:

• "-help" - Displays a short help text.
• "-verbose" - Generates verbose output to standard output.
• "-classpath classpath" - Specifies a list of path names where the compiler will search for compiled type definitions. If "-classpath" is not specified, the current directory will be used as the class path.
• "-sourcepath sourcepath" - Specifies a list of path names where the compiler will search for source type definitions. If "-source" is not specified, the current directory will be used as the source path.
• "-d directory" - Specifies the directory where the compiler will store the generated class files. If "-d" is not specified, the class files will be stored in the same places as the source files.
• "-g | -g:none" - Asks the compiler to generate debugging information into the class files or generates no debugging information at all.

Hello.class - My First Class File

To test the compiler, I wrote the following Java file, Hello.java:

class Hello {
   public static void main(String[] a) {
      System.out.println("Hello world!"); 	
   }
}

Here is what I did in a command window to compile Hello.java into Hello.class:

>javac Hello.java

>dir Hello.*
   416 Hello.class
   116 Hello.java

>java Hello
Hello world!

(Continued on next part...)

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