is used as classpath. This means that when our working directory is D:\myprogram\ (on Linux, /home/user/myprogram/), we would not need to specify the classpath explicitly. When overriding however, it is advised to include the current folder "." into the classpath in the case when loading classes from current folder is desired. The same applies not only to java launcher but also to javac, the java compiler. Setting the path of a Jar file If a program uses a supporting library enclosed in a Jar file called supportLib.jar, physically located in the directory D:\myprogram\lib\ and the corresponding physical file structure is: D:\myprogram\ | ---> lib\ | ---> supportLib.jar | ---> org\ | --> mypackage\ | ---> HelloWorld.class ---> SupportClass.class ---> UtilClass.class the following command-line option is needed: java -classpath D:\myprogram;D:\myprogram\lib\supportLib.jar org.mypackage.HelloWorld or alternatively: Adding all JAR files in a directory In Java 6 and higher, one can add all jar-files in a specific directory to the classpath using wildcard notation. Windows example: Linux example: This works for both -classpath options and environment classpaths. Setting the path in a manifest file If a program has been enclosed in a Jar file called helloWorld.jar, located directly in the directory D:\myprogram, the directory structure is as follows: D:\myprogram\ | ---> helloWorld.jar | ---> lib\ | ---> supportLib.jar The manifest file defined in helloWorld.jar has this definition: The manifest file should end with either a new line or carriage return. The program is launched with the following command: java -jar D:\myprogram\helloWorld.jar [app arguments] This automatically starts org.mypackage.HelloWorld specified in class Main-Class with the arguments. The user cannot replace this class name using the invocation . Class-Path describes the location of supportLib.jar relative to the location of the library helloWorld.jar. Neither absolute file path, which is permitted in parameter on the command line, nor jar-internal paths are supported. This means that if the main class file is contained in a jar, org/mypackage/HelloWorld.class must be a valid path on the root within the jar. Multiple classpath entries are separated with spaces: OS specific notes Being closely associated with the file system, the command-line Classpath syntax depends on the operating system. For example: on all Unix-like operating systems (such as Linux and Mac OS X), the directory structure has a Unix syntax, with separate file paths separated by a colon (":"). on Windows, the directory structure has a Windows syntax, and each file path must be separated by