JDBC written question and answer

1.    What is JDBC?

JDBC is a layer of abstraction that allows users to choose between databases. It allows you to change to a different database engine and to write to a single API. JDBC allows you to write database applications in Java without having to concern yourself with the underlying details of a particular database.

2.    What are the common tasks or steps of JDBC?

1. Create an instance of a JDBC driver or load JDBC drivers through jdbc.drivers;
2. Register a driver;
3. Specify a database;
4. Open a database connection;
5. Submit a query;
6. Receive results

3.    What Class.forName will do while loading drivers of JDBC?

It is used to create an instance of a driver and register it with the DriverManager. When you have loaded a driver, it is available for making a connection with a DBMS.

4.    Difference between PreparedStatement & Statement?

preparedstatement extends statement with added advantage of taking the arguments at run time.

preparedStatement pstmt =con.prepareStatement("update FIRST_TABLE set job_code = ? where name = ? ");

pstmt.setInt(1,2); pstmt.setString(2,"JOHN");

When the PreparedStatement is executed, the DBMS can just run the PreparedStatement ’s SQL statement without having to compile it first.

Statement is used to execute static queries in the databases. It can’t take the parameters at run time.

stmt.executeQuery("select * from FIRST_TABLE");

5.    What is SQLException?

The SQLException class and its subtypes provide information about errors and warnings that occur while a data source is being accessed.

The base class for exceptions that occur while running JDBC applications is SQLException. Every method of the JDBC API is declared as being able to throw SQLExceptions. SQLException is an extension of java.lang.Exception and provides additional information related to failures that happen in a database context. Specifically, the following information is available from an SQLException:

• Text description
• SQLState
• Error code
• A reference to any other exceptions that also occurred

6.    What is ResultSet object?

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.

A default ResultSet object is not updatable and has a cursor that moves forward only. Thus, we can iterate through it only once and only from the first row to the last row. It is possible to produce ResultSet objects that are scrollable and/or updatable.

7.    What packages are used by JDBC?

There are 8 packages: java.sql.Driver, Connection,Statement, PreparedStatement, CallableStatement, ResultSet, ResultSetMetaData, DatabaseMetaData.

8.    What is the difference between executequery () and executeupdate ()?

executeQuery() - is for operation select of Sql by PreparedStatement or Statement.

executeUpdata()- is for the operations such as insert, update or delete on SQL by PreparedStatement or Statement.

9.    What is TableModel?

The TableModel interface specifies the methods the JTable will use to interrogate a tabular data model.

The JTable can be set up to display any data model which implements the TableModel interface with a couple of lines of code:

   TableModel myData = new TableModel(); 

   JTable table = new JTable(myData);

10. What is DefaultMutableTreeNode & DefaultTreeModel?

A DefaultMutableTreeNode is a general-purpose node in a tree data structure. DefaultMutableTreeNode provides operations for examining and modifying a node's parent and children and also operations for examining the tree that the node is a part of. This class provides enumerations for efficiently traversing a tree or subtree in various orders or for following the path between two nodes. A DefaultMutableTreeNode may also hold a reference to a user object, the use of which is left to the user. Asking a DefaultMutableTreeNode for its string representation with toString() returns the string representation of its user object.

DefaultTreeModel  is a simple tree data model that uses TreeNodes.

Evidence Question for JDBC:

• a. Create a database named inventory in MySql using the command prompt.
  
  b. Create a table named product in that database with required field and data types to store the product list from the application.
  
  c. In NetBeans, create a project and create necessary frames to purchase and sale product. The product quantity should be updated properly after purchase and sale a product. Display the product quantity on hand of specific product.
  
  d. Display all product lists in a table on a frame.