filename

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
复制
Abc/file.txt
输出
复制
txt

import java.util.Scanner;

public class HW04 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String str = in.nextLine();

        String result;

        int begin = str.lastIndexOf('.');

        if(begin == -1){
            System.out.println("null");
        }else {
            result = str.substring(begin + 1, str.length());
            System.out.println(result);
        }

    }
}