字节流的操作

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();
    }
}