Java is a very popular object-oriented programming language. As such, there is no definite answer to this. Java can be learned easily even without certifications. You can become a successful Java developer even without any certifications. But, if you wish to master Java without certification, then you should very thorough with Java Fundamentals and advanced Java concepts as well.
But, pursuing certification is also an added advantage. And Oracle provides below certifications.
Here is the links for how to prepare for OCAJP and OCPJP:
Here is the list of all the certifications offered for a Java developer.
Oracle Certified Associate (OCA)
Oracle Certified Professional (OCP)
- Java Programmer II
- Java Developer
Oracle Certified Expert (OCE)
- Web Component Develper
- Business Component Developer
- Java Persistence Developer
- Java Server Faces Developer
- Web Services Developer
Oracle Certified Master (OCM)
- Java EE Enterprise Architect
Hope this helps you :)