How to delete autorun.inf with command prompt
attrib -s -h -r autorun.inf
del autorun.inf
Removing Autorun.inf Virus & Viruses that uses Autorun.INF
There are several viruses that uses the autorun.inf to spread itself such as the Bacalid (hides itself in ctfmon.exe) and the RavMon.EXE. These viruses set its file attributes to System+Hidden+Read-Only attributes so some anti-viruses will have a hard time detecting or finding them. These viruses save itself in the root directory of every available drives of the current infected computer and runs itself every time you Double-Click the drive. In USB Sticks and CDs that are infected by the virus runs automatically especially if drive autorun is enabled for the current drives (which is usually by default, autorun for drives are enabled).
Autorun.INF is usually used by CD Installers to autoplay their installations but Hard disks by default should not have AUTORUN.INF in the drive.
Now, it is possible that your computer is infected by those viruses if you try to display the content of the your computer through command prompt, using the dir /ah command. You will see the following window if you try this:
You will see from this window that drive C contains a hidden file autorun.inf, this is a possibility that the computer is infected. Now to erase this, restart your window to Safe Mode Command Prompt. (Do this by rebooting your computer and pressing F8 before windows go out and select from the boot menu). On drive C and other drives type the following commands: 1. attrib -h -r -s autorun.inf 2. del autorun.inf
Do this steps to other drives to disable the autorun.inf .
Disable AUTORUN from Registry
Now you can disable the AUTORUN for all drives by configuring the registry. Open the registry by typing regedit.exe to the command prompt (if your still at the command prompt) or execute it in Run. Look for the HKEY_CURRENT_USER\Software\ Microsoft\Windows\CurrentVersion\Policies\Explorer as shown below:
Double-click the NoDriveAutorun DWORD entry and type the value HEX: FF (255 in Decimal). (If the NoDriveAutorun does not exists, you can creat it by right-clicking the right side area of the regedit window, then click New->DWord Value -> type NoDriveAutorun) Close the registry and restart the computer. This procedure will disable all the autorun for all drives of your computer and at least will prevent the autorun function of infected USB drives or CDs and avoid the infection of viruses like the Bacalid and RavMon.exe.
Update:
If you want to prevent viruses that uses autorun.inf to infect your USB flash drive, try to do this:
1. Open your flash drive via Command Prompt (do this via Start->Run->cmd.exe)
2. Change your logged drive to your USB flash drive (e.g. if your drive is at drive E: then type E: on the command prompt then press enter)
3. Create a folder named: AUTORUN.INF on the root directory of your flash drive. (to do this type the command: MD\AUTORUN.INF). If an error: a subdirectory already exists… shows, try to follow the instruction above to remove existing autorun.inf before doing this instruction.
The reason why this will avoid future infection is that autorun.inf viruses usually generates a file autorun.inf. Having an AUTORUN.INF folder on the root directory of your drives will make virus programs unable to create their own autorun.inf file, virus can’t even overwrite
Dec 19, 2008
FIX:Drive opens in new window on double click in windows XP Full Why drive opens in new window?
FIX:Drive opens in new window on double click in windows XP Full
Why drive opens in new window?
It happens when a program or virus tries to edit the File Folder or Drive shell entries to add more context menu items and set them as default for double click action.
Lets see how we can fix this.
Fix:
First Method:
1. Open Start >> Run and type regsvr32 /i shell32.dll
2. press ok
3. You will see a message DllRegisterServer and DllInstall in shell32.dll succeeded
4. that’s it
Second Method:
1. Open Start >> Run and type regedit
2. Navigate to HKEY_CLASSES_ROOT/Directory/Shell
3. Double click the default key type none and press ok.
4. now navigate to HKEY_CLASSES_ROOT/Drive/Shell.
5. Double click the default key type none and press ok.
Third Method:
If you don’t want to play with the registry ,you can run the following command instead at
Run Prompt: ( Open Start >> Run )
“reg add hkcr\drive\shell /ve /d none /f” (without double quotes)
We hope at least one of the above method may work for you to fix the trouble, if not please let us know.
Note: If still after following the above you are not able to solve the problem then update your antivirus and run a complete scan and make your system virus free.
Please Download this file...If u Like my Work. This file is Less than 1Kb...It is just a Text file with thanks.
Link: http://www.ziddu.com/downloadlink/2529657/Thanks.txt
Why drive opens in new window?
It happens when a program or virus tries to edit the File Folder or Drive shell entries to add more context menu items and set them as default for double click action.
Lets see how we can fix this.
Fix:
First Method:
1. Open Start >> Run and type regsvr32 /i shell32.dll
2. press ok
3. You will see a message DllRegisterServer and DllInstall in shell32.dll succeeded
4. that’s it
Second Method:
1. Open Start >> Run and type regedit
2. Navigate to HKEY_CLASSES_ROOT/Directory/Shell
3. Double click the default key type none and press ok.
4. now navigate to HKEY_CLASSES_ROOT/Drive/Shell.
5. Double click the default key type none and press ok.
Third Method:
If you don’t want to play with the registry ,you can run the following command instead at
Run Prompt: ( Open Start >> Run )
“reg add hkcr\drive\shell /ve /d none /f” (without double quotes)
We hope at least one of the above method may work for you to fix the trouble, if not please let us know.
Note: If still after following the above you are not able to solve the problem then update your antivirus and run a complete scan and make your system virus free.
Please Download this file...If u Like my Work. This file is Less than 1Kb...It is just a Text file with thanks.
Link: http://www.ziddu.com/downloadlink/2529657/Thanks.txt
Nov 26, 2008
Oct 21, 2008
Sep 28, 2008
MOBILE TECHNOLOGIES" Java - Interview Questions
1. Which two of the following legal objectives for non tested clauses and interfaceA. final abstract class test {}
B. public static interface test {}
C. final public class test {}
D. procted abstract class test {}
E. procted interface class test{}
F. abstract public class test {}
ANSWER: C & F
2. There should be one public class in a file : True/False
ANSWER: True
3. Interface variable are implicity public static final : True/False
ANSWER: True
4. Which two are equal
A. 32/2
B. (82>>2)<<4
C. 2^5
D. 128>>>2
E. (2>>1)*(32>>3)
F. 2>>5
ANSWER: B & E
5. Public class test
{
Public static void main (string args[])
{
signed int x=10;
for (int y=0 ;y<5;y+1,x--)
}
system.out.print(""+x);
}
ANSWER: Compililation fails signed is not keyword
6. Which is the reserved word in jav programming lang
A. method
B. native
C. sublance
D. reference
E. array
ANSWER: B
7. Which class does not orerride the equal and hash coder methods inheriting thisA. java.long.string
B. java.long.double
C. java.long.string buffer
D. java.long.character
E. java.util.arrays
ANSWER: C
8. Which collections class allows you to grow or shrink size and provides indexed access to elements but whose methods are not sync.A. java.util.hashset
B. java.util.linkedhashset
C. java.util.list
D. java.util.Arryalist
E. java.util.vectar
ANSWER: D
9. Which state is true
A. calling runtime.g © will cause objects 1 to be grabage collects
B. the garbge collector uses a marce and sweep alga.
C. if an object can be asssed from a live thread it cant be garbage collected
ANSWER: B & C
9. What is the numerical range of occur
A. -128 to 127
B. -(2^15) to (2^15)-1
C. 0 to 32767
D. platform deiendent
E. 0 to 65535
ANSWER: E
10. What is the most restrictive access modifer that will allow members of one class to have access to membersof another class in same packageA. public
B. abstract
C. protected
D. synchronized
E. defaut acccess
ANSWER: E
11. Given a methed proctected, class what access modifer do you use to restrict access that method to only the other members of the same classA. final
B. static
C. private
D. protected
E. volatile
F. defaut access
ANSWER: C
12. int I= 0
label
if(I<2)
system.out.print("I is" +I);
I++;
continue label
ANSWER: Complution error.
B. public static interface test {}
C. final public class test {}
D. procted abstract class test {}
E. procted interface class test{}
F. abstract public class test {}
ANSWER: C & F
2. There should be one public class in a file : True/False
ANSWER: True
3. Interface variable are implicity public static final : True/False
ANSWER: True
4. Which two are equal
A. 32/2
B. (82>>2)<<4
C. 2^5
D. 128>>>2
E. (2>>1)*(32>>3)
F. 2>>5
ANSWER: B & E
5. Public class test
{
Public static void main (string args[])
{
signed int x=10;
for (int y=0 ;y<5;y+1,x--)
}
system.out.print(""+x);
}
ANSWER: Compililation fails signed is not keyword
6. Which is the reserved word in jav programming lang
A. method
B. native
C. sublance
D. reference
E. array
ANSWER: B
7. Which class does not orerride the equal and hash coder methods inheriting thisA. java.long.string
B. java.long.double
C. java.long.string buffer
D. java.long.character
E. java.util.arrays
ANSWER: C
8. Which collections class allows you to grow or shrink size and provides indexed access to elements but whose methods are not sync.A. java.util.hashset
B. java.util.linkedhashset
C. java.util.list
D. java.util.Arryalist
E. java.util.vectar
ANSWER: D
9. Which state is true
A. calling runtime.g © will cause objects 1 to be grabage collects
B. the garbge collector uses a marce and sweep alga.
C. if an object can be asssed from a live thread it cant be garbage collected
ANSWER: B & C
9. What is the numerical range of occur
A. -128 to 127
B. -(2^15) to (2^15)-1
C. 0 to 32767
D. platform deiendent
E. 0 to 65535
ANSWER: E
10. What is the most restrictive access modifer that will allow members of one class to have access to membersof another class in same packageA. public
B. abstract
C. protected
D. synchronized
E. defaut acccess
ANSWER: E
11. Given a methed proctected, class what access modifer do you use to restrict access that method to only the other members of the same classA. final
B. static
C. private
D. protected
E. volatile
F. defaut access
ANSWER: C
12. int I= 0
label
if(I<2)
system.out.print("I is" +I);
I++;
continue label
ANSWER: Complution error.
Some imp Java Faq's
1. what’s the difference between an interface and an abstract class?
Ans: Interface is pure abstract class that is all the methods are abstract.
In abstract class all the methods need not be abstract.
2. why would you use a synchronized block vs. synchronized method?3. Explain the usage of the keyboard transient?
4. How can you force garbage collection?
Ans: By using the method runtime.gc()
5. what’s the difference between the method sleep( )and wait( )?
Ans:wait() can be used only for synchronized sleep() is irrespective of it.
6. Can you write a java class that could be used both as an applet as well as an application?Ans:Yes
7. what’s the difference between constructors and other methods?Ans: Constructors don’t have any return type whereas methods have.
8. Can you call one constructor from another if a class has multiple constructors?Ans:Yes using the key word “thisâ€.
9. If a class is located in a package , what do you need to change in the OS environment to be able to use it?Ans:We need to change the “ClassPath†variable
10. what would you use to compare two string variables –the operator= = or the method equals?Ans: “equals†(= = is used to compare # code)
11. Does it matter in what order catch statements for FileNotFoundException and IOexception are written?
Ans:Yes.(super class exception should succeed sub class exception so FileNotFoundException should placed before IOexception)
12. what can go wrong if you replace && with & in the following code:
string a = null: if (a!=null && a. length ()>10){…}Ans: (&& is logical operator whereas & bitwise operator)
13. How can a subclass call a method or a constructor defined in a superclass?
Ans:Using the super keyword.
14. Can there be an abstract class with no abstract methods in it?Ans:Yes if the clas itself is declared Abstract.
15. Can an interface have be final?Ans: No.If it is final it can’t be implemented at all.
16. Can an interface have an inner class?Ans: Yes.
17. Can we define private and protected modifiers for variables in interface?Ans:No it has to be public
18. What is a local, member and a class variable?19. what does it mean that a method or fields is “static�
20. what is synchronization and why is it important?21. Is null a keyword?
Ans: No it is the reserved word
22. what is the range of the char type?Ans: ( 0-2^16-1)
23. what is similarities/difference between an abstract class and interface?
24. Explain the user defined exceptions?
25. Differentiate between java and c++?
26. what is a Expression?
27. Is main a keyword in java?
28. If I write system . exit (0); at the end of the try block, will the finally block still execute?
29. what are wrapper classes?
30. what if the static modifier is removed from the signature of the main method?
Ans: Interface is pure abstract class that is all the methods are abstract.
In abstract class all the methods need not be abstract.
2. why would you use a synchronized block vs. synchronized method?3. Explain the usage of the keyboard transient?
4. How can you force garbage collection?
Ans: By using the method runtime.gc()
5. what’s the difference between the method sleep( )and wait( )?
Ans:wait() can be used only for synchronized sleep() is irrespective of it.
6. Can you write a java class that could be used both as an applet as well as an application?Ans:Yes
7. what’s the difference between constructors and other methods?Ans: Constructors don’t have any return type whereas methods have.
8. Can you call one constructor from another if a class has multiple constructors?Ans:Yes using the key word “thisâ€.
9. If a class is located in a package , what do you need to change in the OS environment to be able to use it?Ans:We need to change the “ClassPath†variable
10. what would you use to compare two string variables –the operator= = or the method equals?Ans: “equals†(= = is used to compare # code)
11. Does it matter in what order catch statements for FileNotFoundException and IOexception are written?
Ans:Yes.(super class exception should succeed sub class exception so FileNotFoundException should placed before IOexception)
12. what can go wrong if you replace && with & in the following code:
string a = null: if (a!=null && a. length ()>10){…}Ans: (&& is logical operator whereas & bitwise operator)
13. How can a subclass call a method or a constructor defined in a superclass?
Ans:Using the super keyword.
14. Can there be an abstract class with no abstract methods in it?Ans:Yes if the clas itself is declared Abstract.
15. Can an interface have be final?Ans: No.If it is final it can’t be implemented at all.
16. Can an interface have an inner class?Ans: Yes.
17. Can we define private and protected modifiers for variables in interface?Ans:No it has to be public
18. What is a local, member and a class variable?19. what does it mean that a method or fields is “static�
20. what is synchronization and why is it important?21. Is null a keyword?
Ans: No it is the reserved word
22. what is the range of the char type?Ans: ( 0-2^16-1)
23. what is similarities/difference between an abstract class and interface?
24. Explain the user defined exceptions?
25. Differentiate between java and c++?
26. what is a Expression?
27. Is main a keyword in java?
28. If I write system . exit (0); at the end of the try block, will the finally block still execute?
29. what are wrapper classes?
30. what if the static modifier is removed from the signature of the main method?
Sep 23, 2008
Sep 22, 2008
One night @ call center book download link
One night @ call center download link
http://rapidshare.com/files/143907568/One_Night___The_Call_Center.pdf
Contact me
http://rapidshare.com/files/143907568/One_Night___The_Call_Center.pdf
Contact me
JDBC Interview Questions Part -II
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
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).
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