RandomAccessFile类的使用(随机读取java中的文件)

package coreJava;
 
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;
 
public class RandomAccessFileWriteandRead {
 
    public static void main(String[] args)throws IOException {
        // TODO Auto-generated method stub
 
        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");
        //获取指针的位置：
        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方法一次只能写一个字节。如果要把i写进去的就得写四次
        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动到头部
        raf.seek(0);
 
        //一次性读取
        byte[] buf = new byte[(int)raf.length()];
        raf.read(buf);
        System.out.println(Arrays.toString(buf));
        for(byte b:buf){
            System.out.print(Integer.toHexString(b & 0xff)+"  ");
        }
        String s1 = new String(buf);
        System.out.println(s1);
 
        //关闭文件
        raf.close();
 
    }
 
}