Convert a for loop to concat String into a lambda expression

Question

I have the following for loop which iterates through a list of strings and stores the first character of each word in a StringBuilder. I would like to know how can

Answer 1

Without creating many intermediate String objects you can do it like this:

StringBuilder sb = list.stream()
                       .mapToInt(l -> l.codePointAt(0))
                       .collect(StringBuilder::new, 
                                StringBuilder::appendCodePoint, 
                                StringBuilder::append);

Note that using codePointAt is much better than charAt as if your string starts with surrogate pair, using charAt you may have an unpredictable result.