'javac' - The Java Compiler

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(Continued from previous part...)

"-sourcepath" - Specifying Source Path

If you use a new type, and you don't have the class definition of that type, but you have its source definition, you can use the "-sourcepath sourcepath" option to tell compiler to get that source definition.

Let's use the same source files, Echoer.java and EchoerTest.java, to test this:

>del Echoer.class
>del EchoerTest.class

>javac -verbose -sourcepath . EchoerTest.java
[parsing started EchoerTest.java]
[parsing completed 30ms]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/lang/Object.class)]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/lang/String.class)]
[checking EchoerTest]
[loading .\Echoer.java]
[parsing started .\Echoer.java]
[parsing completed 0ms]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/lang/System.class)]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/io/PrintStream.class)]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/io/FilterOutputStream.class)]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/io/OutputStream.class)]
[wrote EchoerTest.class]
[checking Echoer]
[loading \j2sdk1.5.0\jre\lib\rt.jar(java/lang/StringBuffer.class)]
[wrote .\Echoer.class]
[total 230ms]

>java EchoerTest
!dlrow olleH

Note that:

• I used "-sourcepath ." to specify the current directory as the source path for the compiler to search for the source definition of "Echoer".
• The compiler loaded .\Echoer.java correctly, when Echoer definition was needed.
• The compiler finished EchoerTest compilation first, then continued to compile Echoer.

"-d" - Specifying Output Directory

If you are writing a real Java application, you will organize your Java classes into packages. The Java source files must be stored in a directory with the path names match the package names. For example, if a source file, Some.java, is defined in a package name as: "com.herong.util", it must be stored in a directory named as: .\com\herong\util\Some.java.

By default, "javac" will output the class file in the same directory as the source file. But you could change this default behavior by using the "-d" option. It will make "javac" to output the class files into the specified directory.

To test this option, I wrote the following Java source file: PackagedHello.java

/**
 * PackagedHello.java
 * Copyright (c) 2006 by Dr. Herong Yang, http://www.herongyang.com/
 */
package com.herong.util;
public class PackagedHello {
   public static void main(String[] a) {
      System.out.println("Packaged: Hello world!"); 	
   }
}

Test 1 - Storing PackagedHello.java in the wrong directory:

>dir PackagedHell.*
   264 PackagedHello.java

>javac PackagedHello.java

>dir PackagedHell.*
   459 PackagedHello.class
   264 PackagedHello.java

>java -cp . PackagedHello
Exception in thread "main" java.lang.NoClassDefFoundError: 
   PackagedHello (wrong name: com/herong/util/PackagedHello)

This proves that packaged classes can not be stored in any directory.

(Continued on next part...)

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