Friday, December 2, 2011

code change while switching JDBC library?

When a new vendor implements JDBC api, they create classes implementing the PreparedStatement java interface. They ship the class files of new PreparedStatement classes. They don't need to ship PreparedStatement.class which is a standard one, unchanged. Suppose i want to change my java app to use this vendor, I need to make exactly one SC (source code) change - import the new PreparedStatement class. Note we make no more and no fewer SC changes. That's the the "state of the art" in java.

The C solution to "API standardization" is different but time-honored. For example, if a vendor implements pthreads, they implement pthread_create() function (and structs like pthread_mutex_t) in a new .C file. They ship the binary. Now suppose I want to change my working C application and switch to this vendor, from an older implementation...

Q: what SC changes?
%%A: possibly none. (None means no recompile needed.) When I compile and link, I probably need to pull in the new binary.

Q: Do they have to ship the header file?
%%A: i don't think so. I feel header file is part of the pthreads standard.

Now the interesting bit -- suppose I want to use a vendor with small extensions. SC change is different -- include a slightly different header file, and change my thread function calls slightly. If the SC changes are small enough, it's practically painless.

Now we see a real-world definition of "API" -- If a vendor makes changes that require application SC change, then that impacts the API.

For java, the API includes all members public or protected. For C, it's more about header files.

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