java输入输出流是站在程序的角度来说的。从文件中读取数据用输入流，向文件中写数据用输出流。

package com.janson.day20180827;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;public class TestFileInputStream {    public static void main(String[] args) {        FileInputStream in = null;        int f = 0;        try {            in = new FileInputStream(System.getProperty("user.dir") + "\\src\\com\\janson\\day20180827\\TestFileInputStream.java");        }catch (FileNotFoundException e) {            e.printStackTrace();            System.out.println("找不到指定文件");            System.exit(-1);        }        try {            long num =0L;            while ((f=in.read()) != -1) {                System.out.print((char)f);                num ++;            }            System.out.println("一共读取了"+ num + "个字节");        }catch (IOException e) {            System.out.println("文件读取错误");            System.exit(-1);        }    }}