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JDBC Interview questions

JDBC Interview Questions
Here you can find out a list of interview questions for JDBC. These questions are often asked by the interviewer for JDBC (Java Database Connectivity) interview. We put our maximum effort to make this answers error free. But still there might be some errors. If you feel out any answer given for any question is wrong, please, please inform us by clicking on report bug button provided below.

In this section we are offering interview questions for JDBC only. if you need interview questions for any other java related technologies , please check the relevant sections.

1. What is JDBC?
JDBC technology is an API (included in both J2SE and J2EE releases) that provides cross-DBMS connectivity to a wide range of SQL databases and access to other tabular data sources, such as spreadsheets or flat files. With a JDBC technology-enabled driver, you can connect all corporate data even in a heterogeneous environment

2. What are stored procedures?
A stored procedure is a set of statements/commands which reside in the database. The stored procedure is precompiled. Each Database has it’s own stored procedure language,

3. What is JDBC Driver ?
The JDBC Driver provides vendor-specific implementations of the abstract classes provided by the JDBC API. This driver is used to connect to the database.

4. What are the steps required to execute a query in JDBC?
First we need to create an instance of a JDBC driver or load JDBC drivers, then we need to register this driver with DriverManager class. Then we can open a connection. By using this connection , we can create a statement object and this object will help us to execute the query.

5. What is DriverManager ?
DriverManager is a class in java.sql package. It is the basic service for managing a set of JDBC drivers.

6. What is a ResultSet ?
A table of data representing a database result set, which is usually generated by executing a statement that queries the database.

A ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. The next method moves the cursor to the next row, and because it returns false when there are no more rows in the ResultSet object, it can be used in a while loop to iterate through the result set.

7. What is Connection?
Connection class represents a connection (session) with a specific database. SQL statements are executed and results are returned within the context of a connection.

A Connection object’s database is able to provide information describing its tables, its supported SQL grammar, its stored procedures, the capabilities of this connection, and so on. This information is obtained with the getMetaData method.

8. What does Class.forName return?
A class as loaded by the classloader.

9. What is Connection pooling?
Connection pooling is a technique used for sharing server resources among requesting clients. Connection pooling increases the performance of Web applications by reusing active database connections instead of creating a new connection with every request. Connection pool manager maintains a pool of open database connections.

10. What are the different JDB drivers available?
There are mainly four type of JDBC drivers available. They are:

Type 1 : JDBC-ODBC Bridge Driver – A JDBC-ODBC bridge provides JDBC API access via one or more ODBC drivers. Note that some ODBC native code and in many cases native database client code must be loaded on each client machine that uses this type of driver. Hence, this kind of driver is generally most appropriate when automatic installation and downloading of a Java technology application is not important. For information on the JDBC-ODBC bridge driver provided by Sun.

Type 2: Native API Partly Java Driver- A native-API partly Java technology-enabled driver converts JDBC calls into calls on the client API for Oracle, Sybase, Informix, DB2, or other DBMS. Note that, like the bridge driver, this style of driver requires that some binary code be loaded on each client machine.

Type 3: Network protocol Driver- A net-protocol fully Java technology-enabled driver translates JDBC API calls into a DBMS-independent net protocol which is then translated to a DBMS protocol by a server. This net server middleware is able to connect all of its Java technology-based clients to many different databases. The specific protocol used depends on the vendor. In general, this is the most flexible JDBC API alternative. It is likely that all vendors of this solution will provide products suitable for Intranet use. In order for these products to also support Internet access they must handle the additional requirements for security, access through firewalls, etc., that the Web imposes. Several vendors are adding JDBC technology-based drivers to their existing database middleware products.

Type 4: JDBC Net pure Java Driver – A native-protocol fully Java technology-enabled driver converts JDBC technology calls into the network protocol used by DBMSs directly. This allows a direct call from the client machine to the DBMS server and is a practical solution for Intranet access. Since many of these protocols are proprietary the database vendors themselves will be the primary source for this style of driver. Several database vendors have these in progress.

11. What is the fastest type of JDBC driver?
Type 4 (JDBC Net pure Java Driver) is the fastest JDBC driver. Type 1 and Type 3 drivers will be slower than Type 2 drivers (the database calls are make at least three translations versus two), and Type 4 drivers are the fastest (only one translation).

12. Is 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-threading.

13. What is 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

14. What is 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 certain data.

15. 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.

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3 Responses to “JDBC Interview questions”

  1. What typs of resultSet? Bcz this question ask interview .
    Please replay

  2. Resulset could be defined in three ways.
    TYPE_SCROLL_SENSITIVE (can scroll forward or backward and sensitive to the changes made in the database)
    TYPE_SCROLL_INSENSITIVE ( can scroll forward and backward but insensitive to database changes; It is actually snapshot of database so once data fetched not changed)
    TYPE_FORWARD_ONLY (can move only in forward direction)

  3. Result Set:It is an interface which is available in java.sql package.It can be created in two ways:
    1.Foraward only Result Set(When result set is forward only we can move the cursor only in the forward direction & only once.
    Methods:
    Boolean next();, void close(); etc……..
    Type of result set you want to get will be depending on stmt object you are using
    Statement st=con.createStatement()
    Statement st=con.createStatement(ResultSet.TYPE-FORWARD-ONLY,ResultSet.CONCUR-READ-ONLY)
    RS=ST.executeQuery(sql);

    2.Scrollable Result Set
    When result set is Scrollable we can move the cursor only in the forward direction &and also in the reverse direction.
    Methods.
    Boolean next();,boolean previous(); etc………
    Statement st=con.createStatement(ResultSet.TYPE-SCROLL-SENSITIVE,
    ResultSet.CONCUR-READ-ONLY)
    RS=ST.executeQuery(sql);

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