Should the Data implements Serializable?
I dont think Data need to implements Serializable unless you will send this object / instance through the network.
it already implements DBMain, is it allow to implement more than one DBMain interface?
Yes becos the instruction does not mention anything about multiple inheritance.
inside the Data class, there's a RandomAccessFile object, it doesn't implement Seriliazable, so what should I do?
Why you need to do so?
An object that requires to implement Serializable ONLY IF it will be sent through the network. Will you need to send a RAF object via RMI?
Hope this help.
Nick.
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