When you download IBM Data server driver for JDBC and SQLJ, the tar or zip file (For Example, DB2 V10.1 FP3 driver download is v10.5fp3_jdbc_sqlj.tar.gz file) contains following files:
Wondering which file to use in your application? Let me explain what those files are and you can decide on which file to use for your application.
db2jcc4.jar and db2jcc.jar, both of them are DB2 JDBC driver jar files and are Type 4 JDBC drivers.
db2jcc.jar includes functions in the JDBC 3.0 and earlier specifications. If you plan to use those functions, include the db2jcc.jar in the application CLASSPATH.
db2jcc4.jar includes functions in JDBC 4.0 and later, as well as JDBC 3.0 and earlier specifications. If you plan to use those functions, include the db2jcc4.jar in the application CLASSPATH.
sqlj.jar and sqlj4.jar files are for applications using SQLJ.
Refer: Installing the IBM Data Server Driver for JDBC and SQLJ on DB2 for Linux, UNIX, and Windows