NX:Please analyze the DBAccess interface

[Donald Jack]

Hello,every one
I just downloaded my assignment,but I don't dare to deal with it.
In my instructions.html file,there are a interface DBAccess provided.

package suncertify.db;
public interface DBAccess
{
// Reads a record from the file. Returns an array where each
// element is a record value.
public String [] readRecord(long recNo)
throws RecordNotFoundException;
// Modifies the fields of a record. The new value for field n 
// appears in data[n]. Throws SecurityException
// if the record is locked with a cookie other than lockCookie.
public void updateRecord(long recNo, String[] data, long lockCookie)
throws RecordNotFoundException, SecurityException;
... ...
  

This is the first part of it.
How can I read and update/delete/create records?
The .db file provided is used to read chars/strings or bytes,isn't it?
Best regards, Donald

[Patrick Deng]

Hi, Can you forward a copy of the instruction to me, I want to take a look at it. Thanks a lot.

[Nicholas Cheung]

How can I read and update/delete/create records?

You can use the RandomAccessFile to perform I/O operations.

The .db file provided is used to read chars/strings or bytes,isn't it?

The data in .db file can be extracted according to the Data file format given in the instruction.html.
For example, in my instrcution:

The format of data in the database file is as follows:
Start of file
4 byte numeric, magic cookie value identifies this as a data file
...

So, in your code, you can

RandomAccessFile raf = new RandomAccessFile("db.db", "rw");
int magicCookie = raf.readInt();

Hope this help.
Nick