更多 Java IO & NIO方面的文章，请参见文集《Java IO & NIO》

• Instances of this class support both reading and writing to a random access file.
  支持对文件的随机访问及读写操作。
• A random access file behaves like a large array of bytes stored in the file system. There is a kind of cursor, or index into the implied array, called the file pointer;
  有一个游标或者索引 file pointer，来访问字节数组
• getFilePointer() 得到当前 file pointer
• seek(long pos) 修改当前 file pointer

RandomAccessFile 的使用：

public static void main(String[] args) throws Exception {
    RandomAccessFile raf = new RandomAccessFile("r.txt", "rw");

    raf.writeUTF("你好");
    System.out.println(raf.getFilePointer());
    raf.seek(0);
    String s = raf.readUTF();
    System.out.println(s);
}

输出：

8
你好