Java用方法来显示千分位

Question

用方法把一串数字的千分位显示出来，让从最低位开始，每三位有一个逗号来表示千分位

Answer 1

public class Test {
    public static void main(String []args) {
        String[] arr={"1","12","123","1234","12345","123456","1234567",
                      "1.1","12.12","123.123","1234.1234","12345.12345","123456.123456","1234567.1234567"};
        for(String s : arr)
            System.out.println(convt(s,","));
    }
    static String convt(String s,String sep) {
        if(s.length()==0)
            return s;        
        StringBuilder sb=new StringBuilder();
        int dot=s.indexOf("."),n,len;
        if(dot==-1) {
            n=s.length()/3;
            len=s.length()%3;
        } else {
            n=dot/3;
            len=dot%3;
        }
        if(len==0) {
            n--;
            len=3;
        }
        sb.append(s.substring(0,len));
        while(n>0) {
            sb.append(sep);
            sb.append(s.substring(len,len+3));
            len+=3;
            n-=1;
        }
        if(dot!=-1)
            sb.append(s.substring(dot));
        return sb.toString();
    }
}