While reading this blogpost , i found :
"Regardless of language, I believe that you should know the standard library inside and out. Time and time again (in Clojure) I've solved a problem with an anonymous function, only to later find that the standard library already defined exactly what I needed. ....
start asking yourself: am I doing something unique, or am I doing something that's common enough to be somewhere in the standard library. More often than I expected, the answer is - yes, there's already a fn in the standard library."
this was in the context of clojure but i think its true for any language or a framework (like Android) and i should from now on follow the advice.