JDBC

Question 1

What is database

Answer 1

Collection of information

Question 2

Relational database

Answer 2

Database that uses table to relate the information

Question 3

How many key interfaces we use in JDBC?

Answer 3

4 key interfaces

Question 4

Where does the concrete classes that implement the interfaces comes from?

Answer 4

from JDBC driver

Question 5

what to understand properly among the jars for different databases?

Answer 5

Each databases have different jar files with these classes

Question 6

What are the key interfaces in JDBC?

Answer 6

Driver, Connection, Statement, ResultSet

Question 7

What are the different interfaces mean?

Answer 7

Driver: How to connect to the database
Connection: How to communicate to the database
Statement: How to run the query
ResultSet: Knows what was returned by the SQL queries

Question 8

Where do all the databases classes lies?

Answer 8

java.sql

Question 9

What is the JDBC URL format?

Answer 9

It has three parts:

1. jdbc -> Protocol
2. oracle -> Product/Vendor Name
3. localhost:8080/Ganesh -> DB connection details

all seperated by ‘:’

Question 10

What are the two ways to get a connection?

Answer 10

DriverManager or Datasource

Question 11

What we should use? DriverManager or Datasource?

Answer 11

Datasource.

Datasource is a factory and it has more features than DriverManager. It can pool connections and store database connection outside our application

Question 12

Where does the implementation class for connection exists?

Answer 12

Inside driver jar

Question 13

What is the use of Class.forName()?

Answer 13

It loads a class. It lets the DriverManager use a Driver even if the JAR doesn’t have ‘META-INF/services/java.sql.Driver file’

Question 14

What does the statement represents?

Answer 14

It represents the SQL statement that you want to run using the connection

Question 15

What is the default type of ResultSet

Answer 15

TYPE_FORWARD_ONLY mode

Question 16

What are the three modes of ResultSet type?

Answer 16

1. TYPE_FORWARD_ONLY
2. TYPE_SCROLL_INSENSITIVE
3. TYPE_SCROLL_SENSITIVE

Question 17

What does TYPE_SCROLL_INSENSITIVE and TYPE_SCROLL_SENSITIVE mean? Whats the difference

Answer 17

Both, allow to go through the data in any order either forward or backward. We can even go to a specific spot.

Difference: What happens when the data changes in actual database while we are busy querying.

TYPE_SCROLL_INSENSITIVE- will have a static view of what result set looked like when we queried. - igf data changed in table, you will not see the latest

TYPE_SCROLL_SENSITIVE - We would see the latest data when scrolling through the ResultSet

Question 18

whats not guaranteed with TYPE_SCROLL_SENSITIVE

Answer 18

Most database and database drivers dont support this type

Question 19

What are the different Concurrency mode?

Answer 19

CONCUR_READ_ONLY

CONCUR_UPDATEABLE

Question 20

What is not required in concurrency mode?

Answer 20

Databases and drivers are not required to support concur_updateable.

Question 21

What happens when the mode of scroll/concur mode that we request is not available?

Answer 21

The driver can downgrade you.

Means, if you ask TYPE_SCROLL_SENSITIVE and if it isn’t available, we get TYPE_SCROLL_INSENSITIVE

Similarly if we request CONCUR_UPDATEABLE and if it is not available we get statement that is “CONCUR_READ_ONLY’

Question 22

Which method is used for all update/insert/delete functionalities and return int?

Answer 22

executeUpdate(query)

Question 23

Which query returns a ResultSet and what kind of dml command is used?

Answer 23

execureQuery(query)

Question 24

Which method is used for both Select and Update

Answer 24

execute(sql)

Question 25

How to find whether the data returned is a ResultSet or Int when using query()?

Answer 25

execute() returns boolean. If it is trues, we can get ResultSet else, we can get the count for updated data. stmt. getResulySet() -> ResultSet stmt. getgetUpdateCount() -> count

Question 26

Why we shoud not use Statement and what should we use and why?

Answer 26

PreparedStatement. advantages: Performance, Security, Readability Performance: In most programs, we run similar queries multiple times. Prepared stmt figures out a plan to run SQL well and remembers it Security: It prevents sqlInjection by using setString() or other set methods so that driver takes care of all escaping for us Readablility: we dont want to use string concatenation

Question 27

How to loop through the resultSet?

Answer 27

hasNext() method

Question 28

Explain about the ResultSet and cursor

Answer 28

ResultSet has a cursor, that points to the current location in the data. The cursor starts pointing out the location befroe the resultset. On the first loop iteration, rs.next() returns true and the cursor moves to point to the first data. At the end, rs.next() returns false. The cursor advances past the end of data.

Question 29

JDBC counts starts with one or 0?

Answer 29

1

Question 30

What happens when you attampt to access the colum that doesnt available in DB?

Answer 30

SQL Exception

Question 31

Is there getChar() method?

Answer 31

No

Question 32

What is the method that allows us to go back to previous row in resultset?

Answer 32

previous()

Question 33

Method to get start and end of the resultSet?

Answer 33

first() and last() . both return boolean whether they are successfull in finding the row or not

Question 34

Which methods return void and why?

Answer 34

beforeFirst() and afterLast() method returns void as there is always possibility that they can be in a spot that doesnt have data

Question 35

Which is the method that takes the cursor to the exact row?

Answer 35

absolute(int num). Positive number means, its starts from first and moves the position down to the numbered row. zero means moves the cursor immediately before the first. Negative means counting from the end of the result rather than from beginning

Question 36

Method that helps to move forward or backward the cursor to current position?

Answer 36

relative(int num) method

Question 37

What does relative(int) method returns?

Answer 37

Boolean. Returns true if the cursor points to a data

Question 38

Is it mandatory to close all resources like connection/Resultset/Statement?

Answer 38

No, closing any resource automatically closes the resources that it created. Eg.., Closes Connection, automatically closes Statement and ResultSet Closing the Statement, automatically closes the ResultSet

Question 39

What is more important in closing the resources?

Answer 39

1. The order in which the resources are closed is more important. First, RsultSet must be closed followd by Statement and Connection

Question 40

Very important point to remenmber on ResultSet Closing?

Answer 40

JDBC automatically closes a ResultSet when | you run another SQL statement from the same Statement