JDBC
Interview Question and Answer
JDBC Questions are integral part of any Java interview, I have not seen any Java Interview which is
completed without asking single JDBC Interview question, there are always at least one or two question from JDBC API. Some of the popular questions like Why
you should use PreparedStatement in Java,
Difference between PreparedStatement and CallableStatement in Java and
few questions is related to improving performance of JDBC layer by applying
some JDBC
performance tips. In this article I have summarized few frequently asked
questions in JDBC, they ranges from easy to difficult and beginner to advanced.
Questions like distributed transaction management and 2 phase commit
is tough to answer until you have real experience but mostly asked in various J2EE
interviews. This is not an extensive list of JDBC question answers but
practicing or revising this question before going to any Java interview
certainly helps.
10 JDBC Interview question answer in Java
Here is my list of frequently asked JDBC question in Java, I have triedto provide answer to most of question. If you have any interesting JDBC
question which you have faced and not in this list then please share with us.
Question 1:
What is JDBC?
Answer : One of the first JDBC interview question in most of interviews.
JDBC is java database connectivity as name implies it’s a java API for
communicating to relational database, API has java classes and interfaces using
that developer can easily interact with database. For this we need database
specific JDBC drivers. Some time this also result in followup questions like Difference
between type 2 and type 4 JDBC drivers. See the link for answer.
Question
2: What are the main steps in java to make JDBC connectivity?
Answer : Another beginner level JDBC Interview question, mostly asked on
telephonic interviews. Here are main steps to connect to database.
·
Load the Driver: First step is to load the database specific driver
which communicates with database.
·
Make Connection: Next step is get connection from the database
using connection object, which is used to send SQL statement also and get result
back from the database.
·
Get Statement object: From connection object we can get statement
object which is used to query the database
·
Execute the Query:Using statement object we execute the SQL or
database query and get result set from the query.
·
Close the connection:After getting resultset and all required
operation performed the last step should be closing the database connection.
For complete code example you can
also refere Java
program to connect to Oracle database
Question
3: What is the mean of “dirty read“ in database?
Answer : This kind of JDBC interview question is asked on 2 to 4 years
experience Java programmer, they are expected to familiar with database
transaction and isolation level etc. As the name it self convey the meaning
of dirty read “read the value which may
or may not be correct”. in database when one transaction is executing and
changing some field value same time some another transaction comes and read the
change field value before first transaction commit or rollback the value
,which cause invalid value for that field, this scenario is known as dirty
read.
Question
4: What is 2 phase commit?
Answer : This is one of the most popular JDBC Interview question and
asked at advanced level, mostly to senior Java developers on J2EE interviews.
Two phase commit is used in distributed environment where multiple process take
part in distributed transaction process. In simple word we can understand like
if any transaction is executing and it will effect multiple database then two
phase commit will be used to make all database synchronized with each other.
In two phase commit, commit or rollback is done by two phases:
1.
Commit request phase: in this phase main process or coordinator
process take vote of all other process that they are complete their process
successfully and ready to commit if all the votes are “yes” then they go
ahead for next phase. And if “No “then rollback is performed.
2. Commit phase: according
to vote if all the votes are yes then commit is done.
Similarly when any transaction changes multiple database after execution
of transaction it will issue pre commit
command on each database and all database send acknowledgement and
according to acknowledgement if all are positive transaction will issue the
commit command otherwise rollback is done .
Question
5: What are different types of Statement?
Answer : This is another classical
JDBC interview question. Variants are Difference between Statement,
PreparedStatemetn and CallableStatement in Java. Statement object is used to
send SQL query to database and get result from database, and we get statement
object from connection object.
There are three types of statement:
1.
Statement: it’s a commonly used for getting data from database useful when we are
using static SQL statement at runtime. it will not accept any parameter.
Statement stmt = conn.createStatement( );
ResultSet rs
= stmt.executeQuery();
2.
PreparedStatement: when we are using same SQL statement multiple time
its is useful and it will accept parameter at runtime.
String SQL = "Update
stock SET limit = ? WHERE stockType = ?";
PreparedStatement pstmt =
conn.prepareStatement(SQL);
ResultSet
rs = pstmt.executeQuery();
To learn more about PreparedStatement, see What
is PreparedStatement in Java and Benefits
3.
Callable Statement: when we want to access stored procedures then
callable statement are useful and they also accept runtime parameter. It
is called like this
CallableStatement cs =
con.prepareCall("{call SHOW_SUPPLIERS}");
ResultSet rs = cs.executeQuery();
Question
6: How cursor works in scrollable result set?
Answer : Another tough JDBC Interview
question, not many Java programmer knows about using Cursor in Java.
in JDBC 2.0 API new feature is added to move cursor in resultset backward
forward and also in a particular row .
There are three constant define in result set by which we can move
cursor.
·
TYPE_FORWARD_ONLY: creates a nonscrollable result set, that is,
one in which the cursor moves only forward
·
TYPE_SCROLL_INSENSITIVE : a scrollable result set does
not reflects changes that are made to it while it is open
·
TYPE_SCROLL_SENSITIVE: a scrollable result set reflects changes that are made to it while it
is open
Question
7: What is connection pooling?
Answer : This is also one of the most popular question asked during JDBC
Interviews. Connection pooling is the mechanism by which we reuse the recourse
like connection objects which are needed to make connection with database .In
this mechanism client are not required every time make new connection and then
interact with database instead of that connection objects are stored in
connection pool and client will get it from there. so it’s a best way to share
a server resources among the client and enhance the application performance. If
you use Spring framework, then you can also refer How
to setup JDBC Connection Pool using Spring in Java
Question
8: What do you mean by cold backup, hot backup?
Answer : This question is not directly related to JDBC but some time
asked during JDBC interviews. Cold back is the backup techniques in which
backup of files are taken before the database restarted. In hot backup backup
of files and table is taken at the same time when database is running. A warm
is a recovery technique where all the tables are locked and users cannot access
at the time of backing up data.
Question
9: What are the locking system in JDBC
Answer : One more tough JDBC question to understand and prepare. There
are 2 types of locking in JDBC by which we can handle multiple user issue using
the record. if two user are reading the same record then there is no issue but
what if users are updating the record , in this case changes done by first user
is gone by second user if he also update the same record .so we need some type
of locking so no lost update.
Optimistic
Locking: optimistic locking lock the record only when update take place.
Optimistic locking does not use exclusive locks when reading
Pessimistic
locking: in this record are locked as it selects the row to update
Question
10: Does the JDBC-ODBC
Bridge support multiple
concurrent open statements per connection?
Answer: No, we can open only one statement object when using JDBC-ODBC Bridge.
That’s all on this list of 10 JDBC Interview question with answer. As I
said JDBC API and there concepts are integral part of any Java interview and
there is always atleast one question from JDBC. Since most application uses
datbase in backend, JDBC becomes critical for any Java developer.
Other Java Interview articles you may find useful
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