Question

I would like to know if there is a way to lock (prevent) an application from starting.

And i also would like to know if there is a way to prevent a service(application) from starting at boot of the device

…i would like to know because i would like to create an anti-malware app.

Answer 1

I would like to know if there is a way to lock (prevent) an application from starting.

Not in any supported fashion. Anything that does this is malware, and the techniques for doing it are security holes.

And i also would like to know if there is a way to prevent a service(application) from
starting at boot of the device

The user can boot their phone in safe mode (I forget the exact process, but it’s something like holding down the HOME key while turning the phone on).