If you have a lot of commands, you shouldn't put them all in the main class.
Make a new class and have it implement CommandExecutor
Add the following to the class:
@Override
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
}
In your main class add in the onEnable (replace commandName with the name of the command and CommandExecutor with the name of the class):
getCommand("commandName").setExecutor(new CommandExecutor());