5 Free OCAJP 7 and OCPJP7 Mock Exams - Online Practice Test (1Z0-803 and 1Z0-804

Hello guys, today I am going to share a list of free OCAJP7 and OCPJP7 mock exams and online practice tests. If you are preparing for Java SE 7 Programmer 1 or 2 certification or upgrading your existing OCJP 6 exam then this will help you to gauge your progress. As per my experience, the three keys to success in any Java certification is a selection of good books, writing small Java programs to understand concepts, and practicing mock exams. You can see that mock exams are very important to do well on the real exam. They give you much-needed practice as well as some idea about what kind of questions you can expect on real exams. Unfortunately, there are not many good quality free mock exams available for OCAJP7 but I have managed to collect some of them. Earlier, I have shared some OCAJP8 mock exams and received a lot of feedback from my readers about a similar list for OCAJP7 and OCPJP7 exams. This is a smaller list as compared to the previous one but I'll keep adding new mock exams if I come across.

java.lang.numberformatexception for input string null - Cause and Solution

The java.lang.NumberFormatException comes when you try to parse a non-numeric String to Number e.g. Short, Integer, Float, Double etc. For example, if you try to convert . "null" to an integer then you will get NumberFormatException. The error "Exception in thread "main" java.lang.NumberFormatException: For input string: "null" is specifically saying that the String you receive for parsing is not numeric and it's true, "null" is not numeric. Many Java methods which convert String to numeric type e.g. Integer.parseInt() which convert String to int, Double.parseDoble() which convert String to double, and Long.parseLong() which convert String to long throws NumberFormatException to inform that the input String is not numeric.

5 Essential difference between Callable and Runnable interface in Java?

The difference between Callable and Runnable is one of the most frequently asked multi-threading and concurrency interview question in Java world. I remember, it was 2007 when I first heard about Callable interface and that too on a telephonic interview. Till then, I was happy using Runnable to implement threads and just started paying attention to Java 1.5, as most of the application by then using Java 1.4. That one interview question encouraged me to learn more about several other useful features introduced in Java 5 concurrency library e.g. CountDownLatch, CyclicBarrier, Semaphore, Atomic variables, and Thread pool. This is one of the reasons I always encourage Java developer to give/take regular interviews, just to update your knowledge.