31) What separates one tier from another in the context of n-tiered architecture?
It depends on the application.
In a web application, for example, where tier 1 is a web-server, it may communicate with a tier 2 Application Server using RMI over IIOP, and subsequently tier 2 may communicate with tier 3 (data storage) using JDBC, etc.
Each of these tiers may be on separate physical machines or they may share the same box.
The important thing is the functionality at each tier.
* Tier 1 - Presentation - should be concerned mainly with display of user interfaces and/or data to the client browser or client system.
* Tier 2 - Application - should be concerned with business logic
Tier 3+ - Storage/Enterprise Systems - should be focused on data persistence and/or communication with other Enterprise Systems.
32) What areas should I focus on for the best performance in a JDBC application?
These are few points to consider:
* Use a connection pool mechanism whenever possible.
* Use prepared statements. These can be beneficial, for example with DB specific escaping, even when used only once.
* Use stored procedures when they can be created in a standard manner. Do watch out for DB specific SP definitions that can cause migration headaches.
* Even though the jdbc promotes portability, true portability comes from NOT depending on any database specific data types, functions and so on.
* Select only required columns rather than using select * from Tablexyz.
* Always close Statement and ResultSet objects as soon as possible.
* Write modular classes to handle database interaction specifics.
* Work with DatabaseMetaData to get information about database functionality.
* Softcode database specific parameters with, for example, properties files.
* Always catch AND handle database warnings and exceptions. Be sure to check for additional pending exceptions.
* Test your code with debug statements to determine the time it takes to execute your query and so on to help in tuning your code. Also use query plan functionality if available.
* Use proper ( and a single standard if possible ) formats, especially for dates.
* Use proper data types for specific kind of data. For example, store birthdate as a date type rather than, say, varchar.
33) How can I insert multiple rows into a database in a single transaction?
//turn off the implicit commit
Connection.setAutoCommit(false);
//..your insert/update/delete goes here
Connection.Commit();
a new transaction is implicitly started.
34) How do I convert a java.sql.Timestamp to a java.util.Date?
While Timesteamp extends Date, it stores the fractional part of the time within itself instead of within the Date superclass. If you need the partial seconds, you have to add them back in.
Date date = new Date(ts.getTime() + (ts.getNanos() / 1000000 ));
35) What is SQL?
SQL is a standardized language used to create, manipulate, examine, and manage relational databases.
36) Is Class.forName(Drivername) the only way to load a driver? Can I instantiate the Driver and use the object of the driver?
Yes, you can use the driver directly. Create an instance of the driver and use the connect method from the Driver interface. Note that there may actually be two instances created, due to the expected standard behavior of drivers when the class is loaded.
37) What's new in JDBC 3.0?
Probably the new features of most interest are:
* Savepoint support
* Reuse of prepared statements by connection pools
* Retrieval of auto-generated keys
* Ability to have multiple open ResultSet objects
* Ability to make internal updates to the data in Blob and Clob objects
* Ability to Update columns containing BLOB, CLOB, ARRAY and REF types
* Both java.sql and javax.sql ( JDBC 2.0 Optional Package ) are expected to be included with J2SE 1.4.
38) Why do I get the message "No Suitable Driver"?
Often the answer is given that the correct driver is not loaded. This may be the case, but more typically, the JDBC database URL passed is not properly constructed. When a Connection request is issued, the DriverManager asks each loaded driver if it understands the URL sent. If no driver responds that it understands the URL, then the "No Suitable Driver" message is returned.
39) When I create multiple Statements on my Connection, only the current Statement appears to be executed. What's the problem?
All JDBC objects are required to be threadsafe. Some drivers, unfortunately, implement this requirement by processing Statements serially. This means that additional Statements are not executed until the preceding Statement is completed.
40) Can a single thread open up mutliple connections simultaneously for the same database and for same table?
The general answer to this is yes. If that were not true, connection pools, for example, would not be possible. As always, however, this is completely dependent on the JDBC driver.
You can find out the theoretical maximum number of active Connections that your driver can obtain via the DatabaseMetaData.getMaxConnections method.
41) Can I ensure that my app has the latest data?
Typically an application retrieves multiple rows of data, providing a snapshot at an instant of time. Before a particular row is operated upon, the actual data may have been modified by another program. When it is essential that the most recent data is provided, a JDBC 2.0 driver provides the ResultSet.refreshRow method.
42) What does normalization mean for java.sql.Date and java.sql.Time?
These classes are thin wrappers extending java.util.Date, which has both date and time components. java.sql.Date should carry only date information and a normalized instance has the time information set to zeros. java.sql.Time should carry only time information and a normalized instance has the date set to the Java epoch ( January 1, 1970 ) and the milliseconds portion set to zero.
43) What's the best way, in terms of performance, to do multiple insert/update statements, a PreparedStatement or Batch Updates?
Because PreparedStatement objects are precompiled, their execution can be faster than that of Statement objects. Consequently, an SQL statement that is executed many times is often created as a PreparedStatement object to increase efficiency.
A CallableStatement object provides a way to call stored procedures in a standard manner for all DBMSes. Their execution can be faster than that of PreparedStatement object.
Batch updates are used when you want to execute multiple statements together. Actually, there is no conflict here. While it depends on the driver/DBMS engine as to whether or not you will get an actual performance benefit from batch updates, Statement, PreparedStatement, and CallableStatement can all execute the addBatch() method.
44) What is JDO?
JDO provides for the transparent persistence of data in a data store agnostic manner, supporting object, hierarchical, as well as relational stores.
45) What is the difference between setMaxRows(int) and SetFetchSize(int)? Can either reduce processing time?
setFetchSize(int) defines the number of rows that will be read from the database when the ResultSet needs more rows. The method in the java.sql.Statement interface will set the 'default' value for all the ResultSet derived from that Statement; the method in the java.sql.ResultSet interface will override that value for a specific ResultSet. Since database fetches can be expensive in a networked environment, fetch size has an impact on performance.
setMaxRows(int) sets the limit of the maximum nuber of rows in a ResultSet object. If this limit is exceeded, the excess rows are "silently dropped". That's all the API says, so the setMaxRows method may not help performance at all other than to decrease memory usage. A value of 0 (default) means no limit.
46) What is DML?
DML is an abbreviation for Data Manipulation Language. This portion of the SQL standard is concerned with manipulating the data in a database as opposed to the structure of a database. The core verbs for DML are SELECT, INSERT, DELETE, UPDATE, COMMIT and ROLLBACK.
47) What is DDL?
DDL is an abbreviation for Data Definition Language. This portion of the SQL standard is concerned with the creation, deletion and modification of database objects like tables, indexes and views. The core verbs for DDL are CREATE, ALTER and DROP. While most DBMS engines allow DDL to be used dynamically ( and available to JDBC ), it is often not supported in transactions.
48) How can I get information about foreign keys used in a table?
DatabaseMetaData.getImportedKeys() returns a ResultSet with data about foreign key columns, tables, sequence and update and delete rules.
49) How do I disallow NULL values in a table?
Null capability is a column integrity constraint, normally aplied at table creation time. Note that some databases won't allow the constraint to be applied after table creation. Most databases allow a default value for the column as well. The following SQL statement displays the NOT NULL constraint:
CREATE TABLE CoffeeTable (
Type VARCHAR(25) NOT NULL,
Pounds INTEGER NOT NULL,
Price NUMERIC(5, 2) NOT NULL
)
50) What isolation level is used by the DBMS when inserting, updating and selecting rows from a database?
The answer depends on both your code and the DBMS. If the program does not explicitly set the isolation level, the DBMS default is used. You can determine the default using DatabaseMetaData.getDefaultTransactionIsolation() and the level for the current Connection with Connection.getTransactionIsolation(). If the default is not appropriate for your transaction, change it with Connection.setTransactionIsolation(int level).
Contact me If any further Information
Showing posts with label JDBC Interview Questions. Show all posts
Showing posts with label JDBC Interview Questions. Show all posts
Sep 22, 2008
JDBC Inteview Questions Part-1
Q What is JDBC?
A
JDBC technology is an API (included in both J2SE and J2EE releases) that provides cross-DBMS connectivity to a wide range of SQL databases and access to other tabular data sources, such as spreadsheets or flat files. With a JDBC technology-enabled driver, you can connect all corporate data even in a heterogeneous environment
2 Q What are stored procedures?
A : A stored procedure is a set of statements/commands which reside in the database. The stored procedure is precompiled. Each Database has it's own stored procedure language,
3 Q What is JDBC Driver ?
A The JDBC Driver provides vendor-specific implementations of the abstract classes provided by the JDBC API. This driver is used to connect to the database.
4 Q What are the steps required to execute a query in JDBC?
A First we need to create an instance of a JDBC driver or load JDBC drivers, then we need to register this driver with DriverManager class. Then we can open a connection. By using this connection , we can create a statement object and this object will help us to execute the query.
5 Q What is DriverManager ?
A DriverManager is a class in java.sql package. It is the basic service for managing a set of JDBC drivers.
6 Q What is a ResultSet ? A
A table of data representing a database result set, which is usually generated by executing a statement that queries the database.
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.
7 Q What is Connection?
A Connection class represents a connection (session) with a specific database. SQL statements are executed and results are returned within the context of a connection.
A Connection object's database is able to provide information describing its tables, its supported SQL grammar, its stored procedures, the capabilities of this connection, and so on. This information is obtained with the getMetaData method.
8 Q What does Class.forName return?
A A class as loaded by the classloader.
9 Q What is Connection pooling?
A Connection pooling is a technique used for sharing server resources among requesting clients. Connection pooling increases the performance of Web applications by reusing active database connections instead of creating a new connection with every request. Connection pool manager maintains a pool of open database connections.
10 Q What are the different JDB drivers available? A There are mainly four type of JDBC drivers available. They are:
Type 1 : JDBC-ODBC Bridge Driver - A JDBC-ODBC bridge provides JDBC API access via one or more ODBC drivers. Note that some ODBC native code and in many cases native database client code must be loaded on each client machine that uses this type of driver. Hence, this kind of driver is generally most appropriate when automatic installation and downloading of a Java technology application is not important. For information on the JDBC-ODBC bridge driver provided by Sun.
Type 2: Native API Partly Java Driver- A native-API partly Java technology-enabled driver converts JDBC calls into calls on the client API for Oracle, Sybase, Informix, DB2, or other DBMS. Note that, like the bridge driver, this style of driver requires that some binary code be loaded on each client machine.
Type 3: Network protocol Driver- A net-protocol fully Java technology-enabled driver translates JDBC API calls into a DBMS-independent net protocol which is then translated to a DBMS protocol by a server. This net server middleware is able to connect all of its Java technology-based clients to many different databases. The specific protocol used depends on the vendor. In general, this is the most flexible JDBC API alternative. It is likely that all vendors of this solution will provide products suitable for Intranet use. In order for these products to also support Internet access they must handle the additional requirements for security, access through firewalls, etc., that the Web imposes. Several vendors are adding JDBC technology-based drivers to their existing database middleware products.
Type 4: JDBC Net pure Java Driver - A native-protocol fully Java technology-enabled driver converts JDBC technology calls into the network protocol used by DBMSs directly. This allows a direct call from the client machine to the DBMS server and is a practical solution for Intranet access. Since many of these protocols are proprietary the database vendors themselves will be the primary source for this style of driver. Several database vendors have these in progress.
11 Q What is the fastest type of JDBC driver?
A
Type 4 (JDBC Net pure Java Driver) is the fastest JDBC driver. Type 1 and Type 3 drivers will be slower than Type 2 drivers (the database calls are make at least three translations versus two), and Type 4 drivers are the fastest (only one translation).
12 Q Is the JDBC-ODBC Bridge multi-threaded?
A No. The JDBC-ODBC Bridge does not support multi threading. The JDBC-ODBC Bridge uses synchronized methods to serialize all of the calls that it makes to ODBC. Multi-threaded Java programs may use the Bridge, but they won't get the advantages of multi-threading.
13 Q What is cold backup, hot backup, warm backup recovery?
A : Cold backup means all these files must be backed up at the same time, before the database is restarted. Hot backup (official name is 'online backup' ) is a backup taken of each tablespace while the database is running and is being accessed by the users
14 Q What is the advantage of denormalization?
A : Data denormalization is reverse procedure, carried out purely for reasons of improving performance. It maybe efficient for a high-throughput system to replicate data for certain data.
15 Q How do you handle your own transaction ?
A :Connection Object has a method called setAutocommit ( boolean flag) . For handling our own transaction we can set the parameter to false and begin your transaction . Finally commit the transaction by calling the commit method.
21) Will a call to PreparedStatement.executeQuery() always close the ResultSet from the previous executeQuery()?
A ResultSet is automatically closed by the Statement that generated it when that Statement is closed, re-executed, or is used to retrieve the next result from a sequence of multiple results.
22) How do I upload SQL3 BLOB & CLOB data to a database?
Although one may simply extract BLOB & CLOB data from the database using the methods of the java.sql.CLOB and java.sql.BLOB, one must upload the data as normal java datatypes. The example below inserts a BLOB in the form of a byte[] and a CLOB in the form of a String into the database
Inserting SQL3 type data [BLOB & CLOB]
private void runInsert() {
try {
// Log
this.log("Inserting values ... ");
// Open a new Statement
PreparedStatement stmnt = conn.prepareStatement(
"insert Lobtest (image, name) values (?, ?)");
// Create a timestamp to measure the insert time
Date before = new java.util.Date();
for(int i = 0; i <>
// Set parameters
stmnt.setBytes(1, blobData);
stmnt.setString(2, "i: " + i + ";" + clobData);
// Perform insert
int rowsAffected = stmnt.executeUpdate();
}
// Get another timestamp to complete the time measurement
Date after = new java.util.Date();
this.log(" ... Done!");
log("Total run time: " + (
after.getTime() - before.getTime()));
// Close database resources
stmnt.close();
} catch(SQLException ex) {
this.log("Hmm... " + ex);
}
}
23) What is the difference between client and server database cursors?
What you see on the client side is the current row of the cursor which called a Result (ODBC) or ResultSet (JDBC). The cursor is a server-side entity only and remains on the server side.
24) Are prepared statements faster because they are compiled? if so, where and when are they compiled?
Prepared Statements aren't actually compiled, but they are bound by the JDBC driver. Depending on the driver, Prepared Statements can be a lot faster - if you re-use them. Some drivers bind the columns you request in the SQL statement. When you execute Connection.prepareStatement(), all the columns bindings take place, so the binding overhead does not occur each time you run the Prepared Statement. For additional information on Prepared Statement performance and binding see JDBC Performance Tips on IBM's website.
25) Is it possible to connect to multiple databases simultaneously? Can one extract/update data from multiple databases with a single statement?
In general, subject, as usual, to the capabilities of the specific driver implementation, one can connect to multiple databases at the same time. At least one driver ( and probably others ) will also handle commits across multiple connections. Obviously one should check the driver documentation rather than assuming these capabilities.
As to the second part of the question, one needs special middleware to deal with multiple databases in a single statement or to effectively treat them as one database. DRDA ( Distributed Relational Database Architecture -- I, at least, make it rhyme with "Gerta" ) is probably most commonly used to accomplish this.
Oracle has a product called Oracle Transparent Gateway for IBM DRDA and IBM has a product called DataJoiner that make multiple databases appear as one to your application. No doubt there are other products available
26) Why do I get an UnsupportedOperationException?
JDBC 2.0, introduced with the 1.2 version of Java, added several capabilities to JDBC. Instead of completely invalidating all the older JDBC 1.x drivers, when you try to perform a 2.0 task with a 1.x driver, an UnsupportedOperationException will be thrown. You need to update your driver if you wish to use the new capabilities.
27) What advantage is there to using prepared statements if I am using connection pooling or closing the connection frequently to avoid resource/connection/cursor limitations?
The ability to choose the 'best' efficiency ( or evaluate tradeoffs, if you prefer, ) is, at times, the most important piece of a mature developer's skillset. This is YAA ( Yet Another Area, ) where that maxim applies. Apparently there is an effort to allow prepared statements to work 'better' with connection pools in JDBC 3.0, but for now, one loses most of the original benefit of prepared statements when the connection is closed. A prepared statement obviously fits best when a statement differing only in variable criteria is executed over and over without closing the statement.
However, depending on the DB engine, the SQL may be cached and reused even for a different prepared statement and most of the work is done by the DB engine rather than the driver. In addition, prepared statements deal with data conversions that can be error prone in straight ahead, built on the fly SQL; handling quotes and dates in a manner transparent to the developer, for example.
28) What is JDBC, anyhow?
JDBC is Java's means of dynamically accessing tabular data, and primarily data in relational databases, in a generic manner, normally using standard SQL statements.
29) Can I reuse a Statement or must I create a new one for each query?
When using a JDBC compliant driver, you can use the same Statement for any number of queries. However, some older drivers did not always "respect the spec." Also note that a Statement SHOULD automatically close the current ResultSet before executing a new query, so be sure you are done with it before re-querying using the same Statement.
30) What is a three-tier architecture?
A three-tier architecture is any system which enforces a general separation between the following three parts:
1. Client Tier or user interface
2. Middle Tier or business logic
3. Data Storage Tier
Applied to web applications and distributed programming, the three logical tiers usually correspond to the physical separation between three types of devices or hosts:
Contact me If any further Information
All The Best
A
JDBC technology is an API (included in both J2SE and J2EE releases) that provides cross-DBMS connectivity to a wide range of SQL databases and access to other tabular data sources, such as spreadsheets or flat files. With a JDBC technology-enabled driver, you can connect all corporate data even in a heterogeneous environment
2 Q What are stored procedures?
A : A stored procedure is a set of statements/commands which reside in the database. The stored procedure is precompiled. Each Database has it's own stored procedure language,
3 Q What is JDBC Driver ?
A The JDBC Driver provides vendor-specific implementations of the abstract classes provided by the JDBC API. This driver is used to connect to the database.
4 Q What are the steps required to execute a query in JDBC?
A First we need to create an instance of a JDBC driver or load JDBC drivers, then we need to register this driver with DriverManager class. Then we can open a connection. By using this connection , we can create a statement object and this object will help us to execute the query.
5 Q What is DriverManager ?
A DriverManager is a class in java.sql package. It is the basic service for managing a set of JDBC drivers.
6 Q What is a ResultSet ? A
A table of data representing a database result set, which is usually generated by executing a statement that queries the database.
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.
7 Q What is Connection?
A Connection class represents a connection (session) with a specific database. SQL statements are executed and results are returned within the context of a connection.
A Connection object's database is able to provide information describing its tables, its supported SQL grammar, its stored procedures, the capabilities of this connection, and so on. This information is obtained with the getMetaData method.
8 Q What does Class.forName return?
A A class as loaded by the classloader.
9 Q What is Connection pooling?
A Connection pooling is a technique used for sharing server resources among requesting clients. Connection pooling increases the performance of Web applications by reusing active database connections instead of creating a new connection with every request. Connection pool manager maintains a pool of open database connections.
10 Q What are the different JDB drivers available? A There are mainly four type of JDBC drivers available. They are:
Type 1 : JDBC-ODBC Bridge Driver - A JDBC-ODBC bridge provides JDBC API access via one or more ODBC drivers. Note that some ODBC native code and in many cases native database client code must be loaded on each client machine that uses this type of driver. Hence, this kind of driver is generally most appropriate when automatic installation and downloading of a Java technology application is not important. For information on the JDBC-ODBC bridge driver provided by Sun.
Type 2: Native API Partly Java Driver- A native-API partly Java technology-enabled driver converts JDBC calls into calls on the client API for Oracle, Sybase, Informix, DB2, or other DBMS. Note that, like the bridge driver, this style of driver requires that some binary code be loaded on each client machine.
Type 3: Network protocol Driver- A net-protocol fully Java technology-enabled driver translates JDBC API calls into a DBMS-independent net protocol which is then translated to a DBMS protocol by a server. This net server middleware is able to connect all of its Java technology-based clients to many different databases. The specific protocol used depends on the vendor. In general, this is the most flexible JDBC API alternative. It is likely that all vendors of this solution will provide products suitable for Intranet use. In order for these products to also support Internet access they must handle the additional requirements for security, access through firewalls, etc., that the Web imposes. Several vendors are adding JDBC technology-based drivers to their existing database middleware products.
Type 4: JDBC Net pure Java Driver - A native-protocol fully Java technology-enabled driver converts JDBC technology calls into the network protocol used by DBMSs directly. This allows a direct call from the client machine to the DBMS server and is a practical solution for Intranet access. Since many of these protocols are proprietary the database vendors themselves will be the primary source for this style of driver. Several database vendors have these in progress.
11 Q What is the fastest type of JDBC driver?
A
Type 4 (JDBC Net pure Java Driver) is the fastest JDBC driver. Type 1 and Type 3 drivers will be slower than Type 2 drivers (the database calls are make at least three translations versus two), and Type 4 drivers are the fastest (only one translation).
12 Q Is the JDBC-ODBC Bridge multi-threaded?
A No. The JDBC-ODBC Bridge does not support multi threading. The JDBC-ODBC Bridge uses synchronized methods to serialize all of the calls that it makes to ODBC. Multi-threaded Java programs may use the Bridge, but they won't get the advantages of multi-threading.
13 Q What is cold backup, hot backup, warm backup recovery?
A : Cold backup means all these files must be backed up at the same time, before the database is restarted. Hot backup (official name is 'online backup' ) is a backup taken of each tablespace while the database is running and is being accessed by the users
14 Q What is the advantage of denormalization?
A : Data denormalization is reverse procedure, carried out purely for reasons of improving performance. It maybe efficient for a high-throughput system to replicate data for certain data.
15 Q How do you handle your own transaction ?
A :Connection Object has a method called setAutocommit ( boolean flag) . For handling our own transaction we can set the parameter to false and begin your transaction . Finally commit the transaction by calling the commit method.
21) Will a call to PreparedStatement.executeQuery() always close the ResultSet from the previous executeQuery()?
A ResultSet is automatically closed by the Statement that generated it when that Statement is closed, re-executed, or is used to retrieve the next result from a sequence of multiple results.
22) How do I upload SQL3 BLOB & CLOB data to a database?
Although one may simply extract BLOB & CLOB data from the database using the methods of the java.sql.CLOB and java.sql.BLOB, one must upload the data as normal java datatypes. The example below inserts a BLOB in the form of a byte[] and a CLOB in the form of a String into the database
Inserting SQL3 type data [BLOB & CLOB]
private void runInsert() {
try {
// Log
this.log("Inserting values ... ");
// Open a new Statement
PreparedStatement stmnt = conn.prepareStatement(
"insert Lobtest (image, name) values (?, ?)");
// Create a timestamp to measure the insert time
Date before = new java.util.Date();
for(int i = 0; i <>
// Set parameters
stmnt.setBytes(1, blobData);
stmnt.setString(2, "i: " + i + ";" + clobData);
// Perform insert
int rowsAffected = stmnt.executeUpdate();
}
// Get another timestamp to complete the time measurement
Date after = new java.util.Date();
this.log(" ... Done!");
log("Total run time: " + (
after.getTime() - before.getTime()));
// Close database resources
stmnt.close();
} catch(SQLException ex) {
this.log("Hmm... " + ex);
}
}
23) What is the difference between client and server database cursors?
What you see on the client side is the current row of the cursor which called a Result (ODBC) or ResultSet (JDBC). The cursor is a server-side entity only and remains on the server side.
24) Are prepared statements faster because they are compiled? if so, where and when are they compiled?
Prepared Statements aren't actually compiled, but they are bound by the JDBC driver. Depending on the driver, Prepared Statements can be a lot faster - if you re-use them. Some drivers bind the columns you request in the SQL statement. When you execute Connection.prepareStatement(), all the columns bindings take place, so the binding overhead does not occur each time you run the Prepared Statement. For additional information on Prepared Statement performance and binding see JDBC Performance Tips on IBM's website.
25) Is it possible to connect to multiple databases simultaneously? Can one extract/update data from multiple databases with a single statement?
In general, subject, as usual, to the capabilities of the specific driver implementation, one can connect to multiple databases at the same time. At least one driver ( and probably others ) will also handle commits across multiple connections. Obviously one should check the driver documentation rather than assuming these capabilities.
As to the second part of the question, one needs special middleware to deal with multiple databases in a single statement or to effectively treat them as one database. DRDA ( Distributed Relational Database Architecture -- I, at least, make it rhyme with "Gerta" ) is probably most commonly used to accomplish this.
Oracle has a product called Oracle Transparent Gateway for IBM DRDA and IBM has a product called DataJoiner that make multiple databases appear as one to your application. No doubt there are other products available
26) Why do I get an UnsupportedOperationException?
JDBC 2.0, introduced with the 1.2 version of Java, added several capabilities to JDBC. Instead of completely invalidating all the older JDBC 1.x drivers, when you try to perform a 2.0 task with a 1.x driver, an UnsupportedOperationException will be thrown. You need to update your driver if you wish to use the new capabilities.
27) What advantage is there to using prepared statements if I am using connection pooling or closing the connection frequently to avoid resource/connection/cursor limitations?
The ability to choose the 'best' efficiency ( or evaluate tradeoffs, if you prefer, ) is, at times, the most important piece of a mature developer's skillset. This is YAA ( Yet Another Area, ) where that maxim applies. Apparently there is an effort to allow prepared statements to work 'better' with connection pools in JDBC 3.0, but for now, one loses most of the original benefit of prepared statements when the connection is closed. A prepared statement obviously fits best when a statement differing only in variable criteria is executed over and over without closing the statement.
However, depending on the DB engine, the SQL may be cached and reused even for a different prepared statement and most of the work is done by the DB engine rather than the driver. In addition, prepared statements deal with data conversions that can be error prone in straight ahead, built on the fly SQL; handling quotes and dates in a manner transparent to the developer, for example.
28) What is JDBC, anyhow?
JDBC is Java's means of dynamically accessing tabular data, and primarily data in relational databases, in a generic manner, normally using standard SQL statements.
29) Can I reuse a Statement or must I create a new one for each query?
When using a JDBC compliant driver, you can use the same Statement for any number of queries. However, some older drivers did not always "respect the spec." Also note that a Statement SHOULD automatically close the current ResultSet before executing a new query, so be sure you are done with it before re-querying using the same Statement.
30) What is a three-tier architecture?
A three-tier architecture is any system which enforces a general separation between the following three parts:
1. Client Tier or user interface
2. Middle Tier or business logic
3. Data Storage Tier
Applied to web applications and distributed programming, the three logical tiers usually correspond to the physical separation between three types of devices or hosts:
Contact me If any further Information
All The Best
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