publicStringJoiner(CharSequence delimiter,
CharSequence prefix,
CharSequence suffix){
Objects.requireNonNull(prefix,"The prefix must not be null");
Objects.requireNonNull(delimiter,"The delimiter must not be null");
Objects.requireNonNull(suffix,"The suffix must not be null");// 进行保护性拷贝,防止分隔符、前缀和后缀在使用过程中在其他代码中被修改