《去哪网编程题》filename extension

题目描述
Please create a function to extract the filename extension from the given path,return the extracted filename extension or null if none.

输入描述:
输入数据为一个文件路径

输出描述:
对于每个测试实例，要求输出对应的filename extension
示例1
输入

Abc/file.txt
输出

txt

解析：注意可能没有扩展名的情况就好了

import java.util.Scanner;/** * Created by Administrator on 2017/8/10. */public class Main {    public static void main(String[] args) {        Scanner sc = new Scanner(System.in);        while (sc.hasNext()){            String s=sc.next();            int index=s.lastIndexOf(".");            if(index==-1){//不包含.就返回-1                System.out.println("null");            }else {                System.out.println(s.substring(index+1));            }        }    }}