Hello.
The EX series fixed switches are coming from factory with all ports preconfigured in access mode in default VLAN i.e. all ports are part of one L2 domain. You can let the EX3300 switch boot and plug 4 cables and end devices will be able to communicate if they are part of same IP subnet network.
However it's recommended to set at least root password on EX switch for security reasons. The management IP, management route and remote management services (SSH / J-WEB) can be beneficial to you too.
See also deafult configuration document: