I learned to write java code (structure, basic io (terminal, file, datastructures) blind like in word or notepad and it would run without errors for a google interview; It is not that much you need to know actually but when you learn it once, it lingers around for quite a long time and it gives you a different feeling of confidence that you actually know java (i was writing java code for 6? years before that already so i do know java).
Its very similiar to my personal experience with doing push ups: If you never have done them you don't have any muscles at certain areas; Now after going from 0 to 15 push ups over a few month, i gained a general better physiology on upper body strenge and it still lingers around.
Non of both are critical in a day to day scenario but both experiences were fun/interesting and this base is now here where it was not before.
It brings me, mentally speaking, closer to really get something like java.