FileInputStream 原理总结 把文件作为字节流进行读操作

package io;

import java.io.FileInputStream;
import java.io.IOException;

public class IOUtil {

    
/**
 * 读取指定文件内容，按照16进制输出到控制台，为什么要按十六进制？
 * 并且每输出10个byte换行
 * @throws IOException 
 */
    public static void printHex(String filename) throws IOException{
        //把文件作为字节流进行读操作
        FileInputStream in = new FileInputStream(filename);//FileInputStream具体实现了在文件上读取数据
      int b;
      int i=1;
      while((b=in.read())!=-1)//b=in.read()这就是程序核心
      {
          System.out.println(Integer.toHexString(b)+"  ");//将整型b转换成16进制表示的字符串？输出
          if(i++%10==0)
          {
              System.out.println();//每隔十个字节换行
          }
      }
    in.close();
    }

}

    /**
     * Reads a byte of data from this input stream. This method blocks
     * if no input is yet available.
     *
     * @return     the next byte of data, or <code>-1</code> if the end of the
     *             file is reached.
     * @exception  IOException  if an I/O error occurs.
     */
    public int read() throws IOException {
        return read0();
    }

    private native int read0() throws IOException;