whats dose ! mean in if (!isEmpty())

the ! exclamation mark, is used in multiple coding languages to negate the following value, mostly used with boolean values.

! true = false ! false = true

weird at the beginning but in some cases its sweet.

if( ! false ) {
   // the code here is executed cause !false = true 
} else {
   // this code is not executed
}

For your example isEmpty() function for sure ( i don't know for sure) returns true or false, with the "!" before, it returns the opposite of the return so to speak !isEmpty() = is not Empty You are checking if something is not Empty ^^

You could also write a second function called "isNotEmpty()" but can save the time and just put a ! in front.

I hope I could helpt, you gonna use the ! in your future for sure a lot of times. I still have to stop and speak "not" out lout that it makes sense to me ^^

greetings patrick

I think it means "if the object is not empty." The object can be a string, array, etc.

http://stackoverflow.com/questions/4845711/difference-between-isempty-and-equals