What the term "reimplement" is? Whether should I rewrite the db.db file gived by SUN?
In the data file format section, there is a sentence that "All numeric values are stored in the header information use the formats of the DataInputStream and DataOutputStream classes. All text values, and all fields (which are text only), contain only 8 bit characters, null terminated if less than the maximum length for the field. The character encoding is 8 bit US ASCII.
All numeric values, like length of column name and so on are bit values
Just make sure that what you are reading / writing is going to be in "US-ASCII" format.