question: default CharSeq join ( CharSequence delimiter , CharSequence prefix , CharSequence suffix ) { StringBuilder stringBuilder = new StringBuilder ( prefix ) ; forEach ( null ) ; stringBuilder . append ( suffix ) ; return CharSeq . of ( stringBuilder . toString ( ) ) ; }
target:  Convert all elements into String, and connect each String together to a single String, following the same order of the seq. Insert a delimiter at each connection point. Add prefix and suffix to the final result.