JDBC Interview Questions And Answers

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Ques: 1 I want to learn java connectivity with oracla.How?

Ans:
You should have Driver for connectivity and 
1) Load that driver in your class
   By help of Class.forNamr(Driver)
2) Than get the connection 
   Connection con = null;
   con =   DriverManger.getDataBaseConnection(url,user,password).
3) Create statement help of connection
   Statement st = con.createStatement("Select * From tbl......");
4) Execute Statement 
     ResultSet rs = null;
      rs= st.execute();
5) Get you result from resultset

Ans:

Ques: 2 How do I retrieve a whole row of data at once, instead of calling an individual ResultSet.getXXX method for each column

Ans:
The ResultSet.getXXX methods are the only way to retrieve data from a ResultSet object, which means that you have to make a method call for each column of a row. It is unlikely that this is the cause of a performance problem, however, because it is difficult to see how a column could be fetched without at least the cost of a function call in any scenario. We welcome input from developers on this issue.

Ques: 3 What are four types of JDBC driver? 

Ans:
Type 1 Drivers
Bridge drivers such as the jdbc-odbc bridge. They rely on an intermediary such as ODBC to transfer the SQL calls to the database and also often rely on native code. It is not a serious solution for an application
Type 2 Drivers
Use the existing database API to communicate with the database on the client. Faster than Type 1, but need native code and require additional permissions to work in an applet. Client machine requires software to run.
Type 3 Drivers
JDBC-Net pure Java driver. It translates JDBC calls to a DBMS-independent network protocol, which is then translated to a DBMS protocol by a server. Flexible. Pure Java and no native code.
Type 4 Drivers
Native-protocol pure Java driver. It converts JDBC calls directly into the network protocol used by DBMSs. This allows a direct call from the client machine to the DBMS server. It doesn’t need any special native code on the client machine.
Recommended by Sun’s tutorial, driver type 1 and 2 are interim solutions where direct pure Java drivers are not yet available. Driver type 3 and 4 are the preferred way to access databases using the JDBC API, because they offer all the advantages of Java technology, including automatic installation. For more info, visit Sun JDBC page

Ques: 4 Is the JDBC-ODBC Bridge multi-threaded? 

Ans:
No. The JDBC-ODBC Bridge does not support concurrent access from different threads. 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. In addition, deadlocks can occur between locks held in the database and the semaphore used by the Bridge. We are thinking about removing the synchronized methods in the future. They were added originally to make things simple for folks writing Java programs that use a single-threaded ODBC driver.

Ques: 5 Does the JDBC-ODBC Bridge support multiple concurrent open statements per connection? 

Ans:
No. You can open only one Statement object per connection when you are using the JDBC-ODBC Bridge.

Ques: 6 How can I retrieve a String or other object type without creating a new object each time? 

Ans:
Creating and garbage collecting potentially large numbers of objects (millions) unnecessarily can really hurt performance. It may be better to provide a way to retrieve data like strings using the JDBC API without always allocating a new object.

Ques: 7 Where can I find info, frameworks and example source for writing a JDBC driver? 

Ans:
There a several drivers with source available, like MM.MySQL, SimpleText Database, FreeTDS, and RmiJdbc. There is at least one free framework, the jxDBCon-Open Source JDBC driver framework. Any driver writer should also review For Driver Writers

Ques: 8 How can I create a custom RowSetMetaData object from scratch? 

Ans:
One unfortunate aspect of RowSetMetaData for custom versions is that it is an interface. This means that implementations almost have to be proprietary. The JDBC RowSet package is the most commonly available and offers the sun.jdbc.rowset.RowSetMetaDataImpl class. After instantiation, any of the RowSetMetaData setter methods may be used. The bare minimum needed for a RowSet to function is to set the Column Count for a row and the Column Types for each column in the row. For a working code example that includes a custom RowSetMetaData.

Ques: 9 How does a custom RowSetReader get called from a CachedRowSet? 

Ans:
The Reader must be registered with the CachedRowSet using CachedRowSet.setReader(javax.sql.RowSetReader reader). Once that is done, a call to CachedRowSet.execute() will, among other things, invoke the readData method.

Ques: 10 What is the fastest type of JDBC driver? 

Ans:
JDBC driver performance will depend on a number of issues:
(a) the quality of the driver code,
(b) the size of the driver code,
(c) the database server and its load,
(d) network topology,
(e) the number of times your request is translated to a different API.

Ques: 11 What is a ResultSet ?

Ans:
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.

Ques: 12 What is Connection pooling?

Ans:
A 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.

Ques: 13 What are the different JDB drivers available?

Ans:
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.

Ques: 14 Is the JDBC-ODBC Bridge multi-threaded?

Ans:
A 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.

Ques: 15 What is cold backup, hot backup, warm backup recovery?

Ans:
A 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

Ques: 16 What is the advantage of denormalization?

Ans:
A 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.

Ques: 17 
How can you retrieve data from the ResultSet?

Ans:
JDBC returns results in a ResultSet object, so we need to declare an instance of the class ResultSet to hold our results. The following code demonstrates declaring the ResultSet object rs.
ResultSet rs = stmt.executeQuery(”SELECT COF_NAME, PRICE FROM COFFEES”);
String s = rs.getString(”COF_NAME”);

Ques: 18 What is DriverManager ?

Ans:
A DriverManager is a class in java.sql package. It is the basic service for managing a set of JDBC drivers.

Ques: 19 What are the different types of Statements?

Ans:
Regular statement (use createStatement method), prepared statement (use prepareStatement method) and callable statement (use prepareCall)
How can you use PreparedStatement? This special type of statement is derived from class Statement.If you need a
Statement object to execute many times, it will normally make sense to use a PreparedStatement object instead. The advantage to this is that in most cases, this SQL statement will be sent to the DBMS right away, where it will be compiled. As a result, the PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled. This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement’s SQL statement without having to compile it first.
PreparedStatement updateSales =
	con.prepareStatement("UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");

Ques: 20 What does setAutoCommit do?

Ans:
When a connection is created, it is in auto-commit mode. This means that each individual SQL statement is treated as a transaction and will be automatically committed right after it is executed. The way to allow two or more statements to be grouped into a transaction is to disable auto-commit mode:
con.setAutoCommit(false);

Once auto-commit mode is disabled, no SQL statements will be committed until you call the method commit explicitly.

con.setAutoCommit(false);
PreparedStatement updateSales =
	con.prepareStatement( "UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");
updateSales.setInt(1, 50); updateSales.setString(2, "Colombian");
updateSales.executeUpdate();
PreparedStatement updateTotal =
	con.prepareStatement("UPDATE COFFEES SET TOTAL = TOTAL + ? WHERE COF_NAME LIKE ?");
updateTotal.setInt(1, 50);
updateTotal.setString(2, "Colombian");
updateTotal.executeUpdate();
con.commit();
con.setAutoCommit(true);

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JDBC Interview Questions And Answers

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