JDBC Interview Questions and Answers

Java Database Connectivity with the acronym of JDBC is known as standard Java API. It is an interface for database-independent in between a broad range of databases and Java programming language. It allows the application programs for the interaction with the database for accessing the data.

Components of Java Database Connectivity are-

• Driver
• Connection
• DriverManager
• SQLException
• Statement
• ResultSet

• Exception handling- In the new features of JDBC 4.0, there is an addition of the abilities to recover from the exceptions by including support for the chained exceptions. These are used for the retrieval of the chained exceptions.
• Driver and connection management- DriverManager with the appropriate DataSource object gives way to the connection retrieval and allows the portability and transparency of the data source instance. There are no requirements of bringing any changes in the application code for building a connection to the different database instance.
• Data type support- Additions of some new data types and the rise in the support for others is another unique feature of JDBC 4.0. Also, new features of the interface, SQLML are added.
• Changes in API- Important and most required API changes have been done here in JDBC 4.0- Array, Connection and PooledConnection, DatabaseMetaData, Wrapper, Statement, PreparerdStatement, and CallableStatement, etc.

This java SE technology is used for building connecting java application with the database. It gets automatically installed with JDK software and used for the communication of Java application to the database in the platform and database independent manner.

• Import JDBC packages and then load in any of the following ways- Class.forName(), DriverManager.registerDriver(). Then register JDBC driver
• Open the connection to the database Connection con= DriverManager.getConnection (url, user, password)
• To perform a query, create a statement object Statement st= con.createStatement ();
• Implement the statement object and then return the query resultset. After that process it.
• Close the resultset, statement objects, and the connection Con.close();

The following are the types of JDBC drivers-

• JDBC-ODBC bridge driver
• Native-API Driver
• All Java+ Middleware translation driver
• Pure Java Driver

DriveManager is a public class in JDBC which is used to extend the Objects classes. The set of JDBC drivers is managed by the essential services provided by DriverManager. The loading of the driver classes referenced in the jdbc.drivers is attempted by it.

The two statements in JDBC, such as PreparedStatement, and CallableStatement are used for defining the properties and the methods for letting the user send PL/SQL or SQL commands. Also, receiving the data from the database and determining the methods for bridging the data type differences become comfortable with the statement interfaces.

It is used for rolling back the transactions or committing them explicitly. It is like undoing the changes. An action can be rolled back to the same savepoint more than once.

The method is used for executing a query. It returns true if the ResultSet object is the query return. It returns one ResultSet object.

Example

                                                    
Int m = st.executeUpdate(sql);

If (m==1)

System.out.println (“inserted successfully: “+sql);

Else

System.out.println (“insertion failed”);
                                                

In JDBC, carrying out of all the sets of actions in one go is known as a transaction. It is an atomic action in which either all are carried out, or none of them is carried out. Java Transaction API

It is the point to which the transaction gets rolled back without affecting the preceding work. The method which is used for setting a savepoint object within the current transaction is Connection.setSavepoint().

There are several JDBC exceptions such as

• Java.sql.BatchUpdateException
• java.sql.SQLException
• java.sql.DataTruncation
• java.sql.SQLWarning

Package Javax.sql is used for JDBC application.

Connection pooling is a maintained cache of database connections which are kept to be used for the future use of the database requests arise. It helps in improving the performance of the commands to be executed in the database.

The locks are the preventive software mechanism which the other users cannot use the data resource.

Types of locks are there-

• Row and key locks
• Page Locks
• Table locks
• Database locks

It is a standardized protocol assuring the implementation of a database commit in such a situation where the commit operation has to be broken into 2 parts. Saving the changes in the database is called commit whereas, rollback is undoing the changes. In the first phase of the commit, data is written into the data records by the servers needing commit data to the log. In the next step, it begins after getting the successful message from the previous phase, and the particular object, i.e., the coordinator, sends a signal to each server with the instructions of the commit.

There are three types of ResultSet in JDBC, namely

• Forward-only
• Scroll-insensitive
• Scroll-sensitive