public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String str = scanner.next(); int i; //使用可变字符串StringBuilder,参数为静态的字符串str StringBuilder str_test=new StringBuilder(str); for(i=str.length()-3;i>=0;i-=3){ //插入"," str_test.insert(i,","); } System.o...