What are the different methods of batch Apex class?

Answer

Database.Batchable interface contains three methods that must be implemented:

1. Start method:
   global (Database.QueryLocator | Iterable<sObject>) start(Database.BatchableContext bc) {}
2. Execute method:
   global void execute(Database.BatchableContext BC, list<P>){}
3. Finish method:
   global void finish(Database.BatchableContext BC){}