更多 Java IO & NIO方面的文章，請參見文集《Java IO & NIO》

• Instances of this class support both reading and writing to a random access file.
  支持對文件的隨機訪問及讀寫操作。
• 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;
  有一個游標或者索引 file pointer，來訪問字節數組
• getFilePointer() 得到當前 file pointer
• seek(long pos) 修改當前 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);
}

輸出：

8
你好