It depends on the knowledge you want to gain.
[Java SE, Java ME and Java EE Basic Skills Required]
Oracle Certified Associate, Java SE 5/SE 6 (Formerly Sun Certified Java Associate (SCJA) ) certification provides basic knowledge required to manage a Java project. The exam also tests your Java EE and Java ME basic skills. You can gain basic knowledge of Object-Oriented Concepts, UML representation of OO concepts, the Java programming language, and general knowledge of Java Platforms and Technologies.
Read this article =>
http://www.epractizelabs.com/blog2/?p=51
[More focused in Java SE 7 Programming]
Oracle Certified Associate, Java SE 7 Programmer certification provides basic knowledge required to program Java code. You need to complete Java SE 7 Programmer I Exam to achieve this certification. You can gain basic knowledge of Java data types, strings, arrays, loop constructs, methods and encapsulation, inheritance and exceptions.
Read this article =>
http://www.epractizelabs.com/blog2/?p=413