java的io中的文件关闭有关问题

import java.io.*;public class TestBufferStream1 {    public static void main(String args[]) {        try        {            FileInputStream fis = new FileInputStream("c:/java/IO/TestFileInputStream.java");            BufferedInputStream bis = new BufferedInputStream(fis);            int c = 0;            System.out.println(bis.read());            System.out.println(bis.read());            bis.mark(100);            for(int i = 0; i < 10 && ((c = bis.read()) != -1); i ++ ) {                System.out.print((char)c + " ");            }            bis.reset();            System.out.println();            for(int i = 0; i < 10 && ((c = bis.read()) != -1); i ++ ) {                System.out.print(c + " ");            }            bis.close();           //为什么fis不用关闭那！？        }        catch (IOException e)        {            e.printStackTrace();        }    }}