Here are the 6 steps to become a certified Java professional:

1. Understand the Java Certification versions and their domain

   Oracle has several versions, categories, and levels of Java Certifications. See this article to find out which one is most suitable for you. As of April 2019, Oracle Certified Java 11 Developer is the most recent version of the Java Certification. However, the older Java 8 version of the certification is also available.
   
   For Java 11, there is no "Associate" level certification. There is just one "Professional" level certification and to get it, you need to pass only one exam - the OCP Java 11 Programmer 1Z0-819 Exam. However, this exam is quite tough because it includes a broad range of topics. They range from basic, such as variable declarations, classes, loops, conditionals, overloading, and overriding) to the really advanced, such as concurrency, annotations, security, JDBC, and NIO. That makes it very tough for beginners.
   
   The OCA 8 exam is relatively easier because it focuses only the basics of the language. If you want to get an Associate level certification, then go for the Oracle Certified Associate, Java SE 8 Programmer certification i.e. OCAJP 8 1Z0-808. The exam for this certification is contains basic Java and object oriented programming questions. You can find detailed information about this certification by visiting the Oracle Certified Associate, Java SE 8 Programmer Certification official web page.
   
   Oracle has come up with an even more basic level of Java certification called Java Foundations Certified Junior Associate (aka JFCJA). This certification is for school going students (Grades 9th to 12th). This is a good certification if you are a Java beginner but we recommend going for the OCAJP certification because OCAJP is a required certification to acquire other higher level certifications. The JFCJA certification path, on the other hand, is a dead end.
   
   If you are already an Oracle Certified Professional Java programmer for an older version of Java such as OCPJP 8/7 or SCJP 6, Oracle offers an upgrade exam (1Z0-817) to upgrade your certification to OCP Java 11 Developer. However, for this, you must have completed the Professional level certification of a previous version i.e. OCP 7/8 or SCJP 6. If you have just completed the Associate level certification (OCA) of a previous version (such as OCAJP 8), the upgrade certification is not for you.

   You may want to check out all the Java SE certification exams that Oracle offers on official web page for all Oracle Java Certification Exams

   Oracle has a habit of changing exam details such as number of questions, pass percentage, and syllabus. So you should always check out the exam details on Oracle official certification page. 

2. Read Recommended Books

   Although Java certifications focus mostly on fundamentals, they do contain topics that are rarely used as well. Therefore, irrespective of how much experience you have, you should go through at least one certification book. Java Certification books make sure you don't miss any important topic that is on the exam.

   • For OCAJP 8 exam, we recommend, "Oracle Certified Associate Java SE 8 Programmer Fundamentals" by Hanumant Deshmukh
     • Amazon Book Information

3. Solve Mock Exams/Sample Tests

   The exams contain tricky questions and even if you have a few years of Java development experience, you will trip while answering the exam questions. Therefore, it is better to prepare by solving as many questions similar to those encountered in the exams as possible. Enthuware offers the best mock exam s/w. It is also very reasonably priced. Usually, people score about 5-10% more on the real exam than what they score on Enthuware mock exams.

4. Register and Buy Vouchers

   To enter a certification exam you need to register with the Oracle Education System and buy an electronic voucher. One exam voucher is nearly $245. It is valid for 6 months from the date of purchase. In case you fail the exam, one can register again after 14 days to retake it.

   Here's the Oracle Education Exam registration link.

5. Locate Exam Place or Take it at Home

   After registration and buying a voucher, when you're ready to take the exam, you can use the Pearsonvue organization to find a suitable place and time to take the exam. Exams may also be rescheduled if need be prior to the exam date.
   
   It is now possible to take the exam online in your home as well. See this for details on how to take the exam in your home.

6. Check Your Results

   Within 30 minutes after taking an exam, you can get your score via email. Therefore, you can learn the outcome of your exam very quickly. After all controls, 3-4 days after, certifications are sent electronically. You can check your eCertificate here.