JItsi meet

Is it possible to limit the number of participants in jitsi meet? lower than the maximum particpants

There is a prosody module which you can configure what to be the max number of participants per room

how about in java form for android videoconference app
? I

This is a server configuration. You need to host your own server and then you can use the prosody module as advised by damencho to limit the number of participants.