This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
In the above function the argument "sharpen" is local to method. It is shadowing the instance variable "sharpen". You are making local variable to NULL. change the argument to any other name as shown below:
void deleteSharpen(Sharpen sharpen1).....you will get output "mothulla"