What is rowset and its Type?

A RowSet is an object that encapsulates a set of rows from either Java Database Connectivity (JDBC) result sets or tabular data sources like a file or spreadsheet. RowSets support component-based development models like JavaBeans, with a standard set of properties and an event notification mechanism.

What are the different types  of RowSet ?

There are two types of RowSet are there. They are:

• Connected - A connected RowSet object connects to the database once and remains connected until the application terminates.
• Disconnected - A disconnected RowSet object connects to the database, executes a query to retrieve the data from the database and then closes the connection. A program may change the data in a disconnected RowSet while it is disconnected. Modified data can be updated in the database after a disconnected RowSet reestablishes the connection with the database.

What are the new features added to JDBC 4.0?

The major features added in JDBC 4.0 include :

• Auto-loading of JDBC driver class
• Connection management enhancements
• Support for RowId SQL type
• DataSet implementation of SQL using Annotations
• SQL exception handling enhancements
• SQL XML support

What is the difference between a Statement and a PreparedStatement?

Statement	PreparedStatement
A standard Statement is used to create a Java representation of a literal SQL statement and execute it on the database.	A PreparedStatement is a precompiled  statement. This means that when the PreparedStatement is executed, the RDBMS can just run the PreparedStatement SQL statement without having to compile it first.
Statement has to verify its metadata against the database every time.	While a prepared statement has to verify its metadata against the database only once.
If you want to execute the SQL statement once go for STATEMENT	If you want to execute a single SQL statement multiple number of times, then go for PREPAREDSTATEMENT. PreparedStatement objects can be reused with passing different values to the queries

What is PreparedStatement?

A prepared statement is an SQL statement that is precompiled by the database. Through precompilation, prepared statements improve the performance of SQL commands that are executed multiple times (given that the database supports prepared statements). Once compiled, prepared statements can be customized prior to each execution by altering predefined SQL parameters.

 PreparedStatement pstmt = conn.prepareStatement("UPDATE EMPLOYEES SET SALARY = ? WHERE ID = ?");
  pstmt.setBigDecimal(1, 153833.00);
  pstmt.setInt(2, 110592);

Here: conn is an instance of the Connection class and "?" represents parameters.These parameters must be specified before execution.

How to create custom exceptions?

A. By extending the Exception class or one of its subclasses.

Example:

class MyException extends Exception {
  public MyException() { super(); }
  public MyException(String s) { super(s); }
  }

What if there is a break or return statement in try block followed by finally block?

If there is a return statement in the try block, the finally block executes right after the return statement encountered, and before the return executes.

What is a DataSource and its Advantages ?

A DataSource object is the representation of a data source in the Java programming language. In basic terms,

• A DataSource is a facility for storing data.
• DataSource can be referenced by JNDI.
• Data Source may point to RDBMS, file System , any DBMS etc..

What are the advantages of DataSource?

The few advantages of data source are :

• An application does not need to hardcode driver information, as it does with the DriverManager.
• The DataSource implementations can easily change the properties of data sources. For example: There is no need to modify the application code when making changes to the database details.
• The DataSource facility allows developers to implement a DataSource class to take advantage of features like connection pooling and distributed transactions.

Which is the right type of driver to use and when?

• Type I driver is handy for prototyping
• Type III driver adds security, caching, and connection control
• Type III and Type IV drivers need no pre-installation

What are the main components of JDBC ?

The life cycle of a servlet consists of the following phases:

• DriverManager: Manages a list of database drivers. Matches connection requests from the java application with the proper database driver using communication subprotocol. The first driver that recognizes a certain subprotocol under JDBC will be used to establish a database Connection.


• Driver: The database communications link, handling all communication with the database. Normally, once the driver is loaded, the developer need not call it explicitly.


• Connection : Interface with all methods for contacting a database.The connection object represents communication context, i.e., all communication with database is through connection object only.


• Statement : Encapsulates an SQL statement which is passed to the database to be parsed, compiled, planned and executed.


• ResultSet: The ResultSet represents set of rows retrieved due to query execution.

Explain the significance of try-catch blocks?

Whenever the exception occurs in Java, we need a way to tell the JVM what code to execute. To do this, we use the try and catch keywords. The try is used to define a block of code in which exceptions may occur. One or more catch clauses match a specific exception to a block of code that handles it.

Why Errors are Not Checked?

A unchecked exception classes which are the error classes (Error and its subclasses) are exempted from compile-time checking because they can occur at many points in the program and recovery from them is difficult or impossible. A program declaring such exceptions would be pointlessly.