Classpath (Java) - Setting The Path To Execute Java Programs - Basic Usage

Basic Usage

Suppose we have a package called org.mypackage containing the classes:

  • HelloWorld (main class)
  • SupportClass
  • UtilClass

and the files defining this package are stored physically under the directory D:\myprogram (on Windows) or /home/user/myprogram (on Linux).

The file structure will look like this:

Microsoft Windows Linux
D:\myprogram\ | ---> org\ | ---> mypackage\ | ---> HelloWorld.class ---> SupportClass.class ---> UtilClass.class /home/user/myprogram/ | ---> org/ | ---> mypackage/ | ---> HelloWorld.class ---> SupportClass.class ---> UtilClass.class

When we invoke Java, we specify the name of the application to run: org.mypackage.HelloWorld. However we must also tell Java where to look for the files and directories defining our package. So to launch the program, we use the following command:

Microsoft Windows Linux
java -classpath D:\myprogram org.mypackage.HelloWorld java -classpath /home/user/myprogram org.mypackage.HelloWorld

where:

  • -classpath D:\myprogram sets the path to the packages used in the program (on Linux, -classpath /home/user/myprogram)
  • org.mypackage.HelloWorld is the name of the main class

Note that if we ran Java in D:\myprogram\ (on Linux, /home/user/myprogram/) then we would not need to specify the classpath since Java implicitly looks in the current working directory for files containing classes.

Read more about this topic:  Classpath (Java), Setting The Path To Execute Java Programs

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