JDBC Interview Questions
How does the JDBC work?
The Java Database Connectivity (JDBC) is used to whenever a Java application
should communicate with a relational database for which a JDBC driver exists.
Main JDBC classes:
DriverManager. Manages a list of database drivers.
Driver. The database communications link, handling all communication with
Connection. Interface with all the methods for contacting a database
Statement. Encapsulates an SQL statement which is passed to the database to
be parsed, compiled, planned and executed.
ResultSet. The answer/result from a statement. A ResultSet is a list which
encapsulates all outgoing results from a given SQL query.
Explain the ways in which we can get runtime information about the JDBC Driver?
Use the following DatabaseMetaData methods:
Explain whether the JDBC-ODBC Bridge multi-threaded?
No. The JDBC-ODBC Bridge does not support multi threading. The JDBC-ODBC
Bridge uses synchronized methods to serialize all of the calls that it makes to ODBC. Multi-
threaded Java programs may use the Bridge, but they won’t get the advantages of multi-
Explain the difference between cold backup, hot backup, warm backup recovery?
Cold backup means all these files must be backed up at the same time, before
the database is restarted. Hot backup (official name is ‘online backup’ ) is a backup taken of
each tablespace while the database is running and is being accessed by the users
What are the advantage of denormalization?
Data denormalization is reverse procedure, carried out purely for reasons of
improving performance. It maybe efficient for a high-throughput system to replicate data for
How do you handle your own transaction ?
Connection Object has a method called setAutocommit ( boolean flag) . For
handling our own transaction we can set the parameter to false and begin your transaction .
Finally commit the transaction by calling the commit method.
Explain whether there is any practical limit for the number of SQL statements that can be
added to an instance of a Statement object ?
While the specification makes no mention of any size limitation for
Statement.addBatch(), this seems to be dependent, as usual, on the driver. Among other things,
it depends on the type of container/collection used. I know of at least one driver that uses a
Vector and grows as needed. I’ve seen questions about another driver that appears to peak
somewhere between 500 and 1000 statements. Unfortunately, there doesn’t appear to be any
metadata information regarding possible limits. Of course, in a production quality driver, one
would expect an exception from an addBatch() invocation that went beyond the command list’s
How can we ensure that the Statement and its ResultSet will be closed on a commit or
Use the DatabaseMetaData methods supportsOpenStatementsAcrossCommit() and
How can we create an updatable ResultSet?
Just as is required with a scrollable ResultSet, the Statement must be
capable of returning an updatable ResultSet. This is accomplished by asking the Connection to
return the appropriate type of Statement using Connection.createStatement(int resultSetType, int
resultSetConcurrency). The resultSetConcurrency parameter must be ResultSet.CONCUR_UPDATABLE.
The actual code would look like this:
Statement stmt = con.createStatement( ResultSet.TYPE_SCROLL_SENSITIVE,
Note that the spec allows a driver to return a different type of
Statement/ResultSet than that requested, depending on capabilities and circumstances, so the
actual type returned should be checked with ResultSet.getConcurrency().
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