I read Kathy Seirra Book which totally focusses on the concepts(Wonderful book),did the self Tests from that book itself,gave two mock tests on certpal.com(Do watch out what mistakes you do),
and reached out many other websites like Niko's Blog(to revise basic things, section wise),Scjptest.com,javagenious.com, etc to name a few
and other sources of mock tests posted on java ranch itself.
Clearing my doubts on javaranch community was really helpful..Please make sure you clear your doubts as you will learn something new from every other doubt you have
TIP::Practice as many questions as you can from whatever source(ONLY after reading the book) beacuse only reading concepts wont help.Applying them on n number of questions
will help memorizing them and
make learning much better and easier.