import java.io.*;class FileStream {    public static void main(String[] args) throws Exception     {        //writeFile();            readFile3();    }    public static void writeFile()throws Exception{        FileOutputStream fos = new FileOutputStream("fos.txt");        fos.write("abcde".getBytes());        fos.close();    }    public static void readFile1()throws Exception{        FileInputStream fis = new FileInputStream("fos.txt");        int ch = 0;        while((ch = fis.read()) != -1){            System.out.println((char)ch);        }        fis.close();    }    public static void readFile2()throws Exception{        FileInputStream fis = new FileInputStream("fos.txt");        byte[] buf = new byte[1024];        int len = 0;        while((len = fis.read(buf)) != -1){            System.out.println(new String(buf, 0, len));        }        fis.close();    }    //available()    //缺点：如果内容过大，容易占用内存，还是以第2种方法为主。    public static void readFile3()throws Exception{        FileInputStream fis = new FileInputStream("fos.txt");        int num = fis.available();        byte[] buf = new byte[num];//定义了一个刚刚好的缓冲区，不用再循环了        fis.read(buf);        System.out.println(new String(buf));        fis.close();    }}