Welcome to the Ranch
To start there are several certs OCA, OCP, OCM for
java. Java pre-6 and Java 7 certs have somewhat different hierarchy.
OCA java associate 5/6 is for non-technical people eg managers or people wanting to enter java
OCP java programmer 5/6 is for more experience java programmers
OCA java programmer 7 is for people wanting to enter java (practically a subset of the OCP java programmer material)
OCP java programmer 7 is for more experience java programmer (the meat of the java cert)
So the question to ask yourself is which version of java you want to pursue? If java 6 go for OCPJP (1 exam), else java 7 (2 exams: OCA+OCP). You can also opt for upgrade to java 7 or even 8 when time is right later by doing java 6.
Hope this helps.