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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