make the ignore file to filter the files that do not need to be committed
[pplymorphism] static method and property can not be overridden.  what if you call a overridden method in the constructor, so in the super constructor you have to call the implementation of the detrived class but the detrived class has not been created yet, what will happen?
[final variable] we can not chage the value of final primitive variavle, we can no t change the reference object of final reference variable but we can change the properties of the final referrence variable
Merge branch 'master' of github.com:bfhuang/ThinkingInJava