It didn't seem that tough to me. The practice exams on jchq.net are very indicative of the level of difficulty.

I didn't have nearly as many questions on Collections as I expected. There was quite a bit on Assertions and a couple on Hashcode. If you read and understand this: http://java.sun.com/j2se/1.4/docs/guide/lang/assert.html you will be fine on the Assertion questions.

I also wish to know about this.