question: public StrBuilder replace ( int startIndex , int endIndex , String replaceStr ) { endIndex = validateRange ( startIndex , endIndex ) ; int insertLen = ( replaceStr == null ? 0 : replaceStr . length ( ) ) ; replaceImpl ( startIndex , endIndex , endIndex - startIndex , replaceStr , insertLen ) ; return this ; }
target:  Replaces a portion of the string builder with another string. The length of the inserted string does not have to match the removed length.