[B&S]is the mode optional?

[he qinfeng]

Hi everyone:
How should I understand the introduction:

"When you submit your assignment, each part (client and server) must be executable using a command of this exact form:
java -jar <path_and_filename> [<mode>]"

it means that the <jarname> is required,the [mode] is optional and all classes of the client and server needn't have the mode flag?
Thanks for your answer.

[Clivant Yeo]

I understand it as you can enter the command line with mode or entered without the mode flag.

[Charlie Goth]

The mode is optional in that the application will run in client mode when no mode is specified.

[he qinfeng]

thank,I understand