How to run this plugin?

[chaiguolong]

Sorry! my English is poor.I hope you can understand.
I don't know how the plugin works.I don't know the specific function of this plugin.I want to set the classpath automatically for java.For example:I set the classpath to demo1, and then compile,run.
when I worked demo2,I should change classpath to demo2.This is too much trouble.
I am not sure if your plugin can help me.If your plugin can not help me.
I hope you can recommend other plugins to me. Thank You!!!

The question:
what is meaning to this code ' \ command! -buffer -nargs=+ -complete=file Java execute '!'.classpath#java_cmd().' '.'.
How to run it.I set 'echo 111111111',but it do not run.