How is import done in Java?

Question

For instance

import org.apache.nutch.plugin.Extension,

though used many times,

I\'ve no much idea what is done essentially.

Answer 1

import org.apache.nutch.plugin.Extension is a compilation time shortcut that allows you to refer to the Extension class without using the class' fully qualified name. It has no meaning at runtime, it's only a compilation time trick to save typing.

By convention the .class file for this class will be located in folder org/apache/nutch/plugin either in the file system or in a jar file, either of which need to be in your classpath, both at compile time and runtime. If the .class file is in a jar file then that jar file needs to be in your classpath. If the .class file is in a folder, then the folder that is the parent of folder "org" needs to be in your classpath. For example, if the class was located in folder c:\myproject\bin\org\apache\nutch\plugin then folder c:\myproject\bin would need to be part of the classpath.

If you're interested in finding out where the class was loaded from when you run your program, use the -verbose:class java command line option. It should tell you which folder or jar file the JVM found the class.