The Java commands section will give you the list of available commands for the Java Client. If in normal mode, all the commands should be available If you're using a restricted Java client, only a few commands are available.
NORMAL
Any /[command] statements not specifically checked for by the client are passed through to the server as-is. For example, /thisisacommand will be passed directly to the server even though the client does not recognize it - maybe the server will.
RESTRICTED
Restricted mode only allows a connection to a single room. If the client is currently in a room and a new room is joined, the current room will be parted.
Available commands:
ACTION - Type an action in the room.
CLEAR - Clear your window.
EMBED - Embed the client in a web page if it is floating.
FLOAT - Detach the client if it is embedded in a web page.
LIST - Retrieve a list of available rooms on the server.
ME - Type an action in the room.
NAMES - Retrieve a list of nicknames in the room.
NICK - Change your current nickname to a new one.
QUIT - Disconnect from the chat server.
SOUND - Play a sound in the room.
WHOIS - Receive /whois information on a nickname.
WHOWAS - Get detailed information on a recently online user (Operators Only).
You can restrict the client even more with the help of additional Java Parameters, which you will find in the param help files.
Example:
/sound moo.au