RandomAccessFile基本操作

package com.imooc.io;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;

public class RafDemo {

    /**
     * @param args
     */
    public static void main(String[] args)throws IOException {
        File demo=new File("demo");
        if(!demo.exists())
            demo.mkdir();
        File file=new File(demo,"raf.dat");
        if(!file.exists())
        {
            file.createNewFile();
        }
        RandomAccessFile raf=new RandomAccessFile(file,"rw");
        
        //指针的位置
        System.out.println(raf.getFilePointer());
        
        raf.write(‘A‘);//只写了一个字节
        System.out.println(raf.getFilePointer());
        raf.write(‘B‘);
        
        int i=0x7fffffff;
        //用write方法每次只能写一个字节，如果要把i写进就得写4次
        raf.write(i>>>24);//高8位
        raf.write(i>>>16);
        raf.write(i>>>8);
        raf.write(i);
        System.out.println(raf.getFilePointer());
        
        //可以直接写一个int
        raf.writeInt(i);
        
        
        String s="中";
        byte[] gbk=s.getBytes("gbk");
        raf.write(gbk);
        System.out.println(raf.length());
        
        //读文件，必须把指针移到头部
        raf.seek(0);
        //一次性读取,把文件中的内容都读到字节数组中
        byte[] buf=new byte[(int)raf.length()];
        
        raf.read(buf);
        System.out.println(Arrays.toString(buf));
        String s1=new String(buf,"gbk");
        System.out.println(s1);
        for(byte b:buf)
        {
            System.out.println((Integer.toHexString(b&0xff))+" ");
        }
    }
}