This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
As the strings str1 and str2 were not initialized, they are null. Why after str2 = str1 + str2 I was expected str2 to still be null but the output is: str2 : nullnull str2 == null false and I do not understand why. str1 and str2 are both null not having value "null", so I do not understand from where there is that nullnull value.