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).
Contact me If any further Information
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
Core Java Inteview Questions Part -V
111 Q How does a try statement determine which catch clause should be used to handle an exception?
When an exception is thrown , the catch block of the try statement are examined in the order in which they appear. The first catch block that is capable of handling the exception is executed. The remaining catch blocks are ignored
112 Q How parameters are passed to methods in java program ?
All java method parameters in java are passed by value only. Obviously primitives are passed by value. In case of objects a copy of the reference is passed and so all the changes made in the method will persist.
113 Q If a class doesn't have any constructors, what will happen?
If a class doesn't have a constructor, the JVM will provide a default constructor for the class.
114 Q What will happen if a thread cannot acquire a lock on an object?
It enters to the waiting state until lock becomes available.
115 Q How does multithreading occurring on a computer with a single CPU?
The task scheduler of OS allocates an execution time for multiple tasks. By switching between different executing tasks, it creates the impression that tasks execute sequentially. But actually there is only one task is executed at a time.
116 Q What will happen if you are invoking a thread's interrupt method while the thread is waiting or sleeping?
When the task enters to the running state, it will throw an InterruptedException.
117 Q What are the different ways in which a thread can enter into waiting state?
There are three ways for a thread to enter into waiting state. By invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method.
118 Q What are the the different ways for creating a thread?
A thread can be created by subclassing Thread, or by implementing the Runnable interface.
119 Q What is the difference between creating a thread by extending Thread class and by implementing Runnable interface? Which one should prefer?
When creating a thread by extending the Thread class, it is not mandatory to override the run method (If we are not overriding the run method , it is useless), because Thread class have already given a default implementation for run method. But if we are implementing Runnable , it is mandatory to override the run method. The preferred way to create a thread is by implementing Runnable interface, because it give loose coupling.
120 Q What is coupling?
Coupling is the dependency between different components of a system
121 Q How is an interface?
An interface is a collection of method declarations and constants. In java interfaces are used to achieve multiple inheritance. It sets a behavioral protocol to all implementing classes.
122 Q What is an abstract class?
An abstract class is an incomplete class. An abstract class is defined with the keyword abstract . We cannot create an object of the abstract class because it is not complete. It sets a behavioral protocol for all its child classes.
123 Q How will you define an interface?
An interface is defined with the keyword interface. Eg:
public interface MyInterface { }
124 Q How will you define an abstract class?
An abstract class is defined with the keyword abstract Eg:
public abstract class MyClass { }
125 Q What is any an anonymous class?
A An anonymous class is a local class with no name.
126 Q What is a JVM heap?
The heap is the runtime data area from which memory for all class instances and arrays is allocated. The heap may be of a fixed size or may be expanded. The heap is created on virtual machine start-up.
127 Q What is difference between string and StringTokenizer?
StringTokenizer as its name suggests tokenizes a String supplied to it as an argument to its constructor and the character based on which tokens of that string are to be made. The default tokenizing character is space " ".
128 Q What is the difference between array and ArrayList ?
Array is collection of same data type. Array size is fixed, It cannot be expanded. But ArrayList is a growable collection of objects. ArrayList is a part of Collections Framework and can work with only objects.
129 Q What is difference between java.lang .Class and java.lang.ClassLoader? What is the hierarchy of ClassLoader ?
Class 'java.lang.Class' represent classes and interfaces in a running Java application. JVM construct 'Class' object when class in loaded. Where as a ClassLoader is also a class which loads the class files into memory in order for the Java programs to execute properly. The hierarchy of ClassLoaders is:
Bootstrap ClassLoaders
Extensive ClassLoaders
System Classpath ClassLoaders
Application ClassLoaders
130 Q What is daemon thread?
Theards which are running on the background are called deamon threads. daemon thread is a thread which doesn't give any chance to run other threads once it enters into the run state it doesn't give any chance to run other threads. Normally it will run forever, but when all other non-daemon threads are dead, daemon thread will be killed by JVM
131 Q What is a green thread?
Native threads can switch between threads preemptively. Green threads switch only when control is explicitly given up by a thread ( Thread.yield(), Object.wait(), etc.) or a thread performs a blocking operation (read(), etc.). On multi-CPU machines, native threads can run more than one thread simultaneously by assigning different threads to different CPUs. Green threads run on only one CPU. Native threads create the appearance that many Java processes are running: each thread takes up its own entry in the process table. One clue that these are all threads of the same process is that the memory size is identical for all the threads - they are all using the same memory. The process table is not infinitely large, and processes can only create a limited number of threads before running out of system resources or hitting configured limits.
132 Q What is volatile variable?
A volatile variable is not allowed to have a local copy of a variable that is different from the value currently held in "main" memory. Volatile modifier requests the JVM to always access the shared copy of the variable so the its most current value is always read.
133 Q Why java does not support multiple inheritance?
Because the multiple inheritance causes the redundancy. Also we cannot solve diamond problem.
134 Q What is diamond problem?
The diamond problem is an ambiguity that can occur when a class multiply inherits from two classes that both descend from a common super class
135 Q How many JVM's we can run in a system?
Any number of JVMs can run in a system. Whenever we issue the command 'java' a new JVM will start.
136 Q Why Java is not 100% pure object oriented language?
Because java uses primitives.
137 Q Why ArrayList is faster than Vector?
Because Vector is synchronized. Synchronization reduces the performance.
138 Q What is the security mechnaism used in java?
Java uses sand box security model.
139 Q What is sandbox?
A sandbox is a security mechanism for safely running programs. The sandbox typically provides a tightly-controlled set of resources for guest programs to run in, such as scratch space on disk and memory.
140 Q What is phantom memory?
Phantom memory is the memory that does not exist in reality.
141 Q What is reflection?
Reflection is the process of finding out the different features of a class dynamically.
142 Q What are the differences between JIT and HotSpot?
The Hotspot VM is a collection of techniques, the most important of which is called adaptive optimization. The original JVMs interpreted byte codes one at a time. Second-generation JVMs added a JIT compiler, which compiles each method to native code upon first execution, then executes the native code. Thereafter, whenever the method is called, the native code is executed. The adaptive optimization technique used by Hotspot is a hybrid approach, one that combines byte code interpretation and run-time compilation to native code. Hotspot, unlike a regular JIT compiling VM, doesn't do "premature optimization"
143 Q What are the advantages and disadvantages of reference counting in garbage collection?
An advantage of this scheme is that it can run in small chunks of time closely linked with the execution of the program. These characteristic makes it particularly suitable for real-time environments where the program can't be interrupted for very long time. A disadvantage of reference counting is that it does not detect cycles. A cycle is two or more objects that refer to one another. Another disadvantage is the overhead of incrementing and decrementing the reference count each time. Because of these disadvantages, reference counting currently is out of favor.
144 Q How would you implement a thread pool?
The ThreadPool class is a generic implementation of a thread pool, which takes the following input Size of the pool to be constructed and name of the class which implements Runnable (which has a visible default constructor) and constructs a thread pool with active threads that are waiting for activation. once the threads have finished processing they come back and wait once again in the pool.
145 Q What is the difference between throw and throws clause?
throw is used to throw an exception manually, where as throws is used in the case of checked exceptions, to tell the compiler that we haven't handled the exception, so that the exception will be handled by the calling function.
146 Q What is JAR file?
A JAR file (short for Java Archive) is a ZIP file used to distribute a set of Java classes. It is used to store compiled Java classes and associated metadata that can constitute a program
147 Q What is a classloader?
A class loader is an object that is responsible for loading classes.
148 Q What is the difference between Comparable and Comparator ?
The Comparable is for natural ordering and Comparator is for custom ordering. But we can override the compareTo method of comparable interface to give a custom ordering.
149 Q What is the difference between List, Set and Map?
A Set is a collection that has no duplicate elements. A List is a collection that has an order associated with its elements. A map is a way of storing key/value pairs. The way of storing a Map is similar to two-column table.
150 Q What is the difference between Exception and Error ?
Error is unrecoverable.
When an exception is thrown , the catch block of the try statement are examined in the order in which they appear. The first catch block that is capable of handling the exception is executed. The remaining catch blocks are ignored
112 Q How parameters are passed to methods in java program ?
All java method parameters in java are passed by value only. Obviously primitives are passed by value. In case of objects a copy of the reference is passed and so all the changes made in the method will persist.
113 Q If a class doesn't have any constructors, what will happen?
If a class doesn't have a constructor, the JVM will provide a default constructor for the class.
114 Q What will happen if a thread cannot acquire a lock on an object?
It enters to the waiting state until lock becomes available.
115 Q How does multithreading occurring on a computer with a single CPU?
The task scheduler of OS allocates an execution time for multiple tasks. By switching between different executing tasks, it creates the impression that tasks execute sequentially. But actually there is only one task is executed at a time.
116 Q What will happen if you are invoking a thread's interrupt method while the thread is waiting or sleeping?
When the task enters to the running state, it will throw an InterruptedException.
117 Q What are the different ways in which a thread can enter into waiting state?
There are three ways for a thread to enter into waiting state. By invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method.
118 Q What are the the different ways for creating a thread?
A thread can be created by subclassing Thread, or by implementing the Runnable interface.
119 Q What is the difference between creating a thread by extending Thread class and by implementing Runnable interface? Which one should prefer?
When creating a thread by extending the Thread class, it is not mandatory to override the run method (If we are not overriding the run method , it is useless), because Thread class have already given a default implementation for run method. But if we are implementing Runnable , it is mandatory to override the run method. The preferred way to create a thread is by implementing Runnable interface, because it give loose coupling.
120 Q What is coupling?
Coupling is the dependency between different components of a system
121 Q How is an interface?
An interface is a collection of method declarations and constants. In java interfaces are used to achieve multiple inheritance. It sets a behavioral protocol to all implementing classes.
122 Q What is an abstract class?
An abstract class is an incomplete class. An abstract class is defined with the keyword abstract . We cannot create an object of the abstract class because it is not complete. It sets a behavioral protocol for all its child classes.
123 Q How will you define an interface?
An interface is defined with the keyword interface. Eg:
public interface MyInterface { }
124 Q How will you define an abstract class?
An abstract class is defined with the keyword abstract Eg:
public abstract class MyClass { }
125 Q What is any an anonymous class?
A An anonymous class is a local class with no name.
126 Q What is a JVM heap?
The heap is the runtime data area from which memory for all class instances and arrays is allocated. The heap may be of a fixed size or may be expanded. The heap is created on virtual machine start-up.
127 Q What is difference between string and StringTokenizer?
StringTokenizer as its name suggests tokenizes a String supplied to it as an argument to its constructor and the character based on which tokens of that string are to be made. The default tokenizing character is space " ".
128 Q What is the difference between array and ArrayList ?
Array is collection of same data type. Array size is fixed, It cannot be expanded. But ArrayList is a growable collection of objects. ArrayList is a part of Collections Framework and can work with only objects.
129 Q What is difference between java.lang .Class and java.lang.ClassLoader? What is the hierarchy of ClassLoader ?
Class 'java.lang.Class' represent classes and interfaces in a running Java application. JVM construct 'Class' object when class in loaded. Where as a ClassLoader is also a class which loads the class files into memory in order for the Java programs to execute properly. The hierarchy of ClassLoaders is:
Bootstrap ClassLoaders
Extensive ClassLoaders
System Classpath ClassLoaders
Application ClassLoaders
130 Q What is daemon thread?
Theards which are running on the background are called deamon threads. daemon thread is a thread which doesn't give any chance to run other threads once it enters into the run state it doesn't give any chance to run other threads. Normally it will run forever, but when all other non-daemon threads are dead, daemon thread will be killed by JVM
131 Q What is a green thread?
Native threads can switch between threads preemptively. Green threads switch only when control is explicitly given up by a thread ( Thread.yield(), Object.wait(), etc.) or a thread performs a blocking operation (read(), etc.). On multi-CPU machines, native threads can run more than one thread simultaneously by assigning different threads to different CPUs. Green threads run on only one CPU. Native threads create the appearance that many Java processes are running: each thread takes up its own entry in the process table. One clue that these are all threads of the same process is that the memory size is identical for all the threads - they are all using the same memory. The process table is not infinitely large, and processes can only create a limited number of threads before running out of system resources or hitting configured limits.
132 Q What is volatile variable?
A volatile variable is not allowed to have a local copy of a variable that is different from the value currently held in "main" memory. Volatile modifier requests the JVM to always access the shared copy of the variable so the its most current value is always read.
133 Q Why java does not support multiple inheritance?
Because the multiple inheritance causes the redundancy. Also we cannot solve diamond problem.
134 Q What is diamond problem?
The diamond problem is an ambiguity that can occur when a class multiply inherits from two classes that both descend from a common super class
135 Q How many JVM's we can run in a system?
Any number of JVMs can run in a system. Whenever we issue the command 'java' a new JVM will start.
136 Q Why Java is not 100% pure object oriented language?
Because java uses primitives.
137 Q Why ArrayList is faster than Vector?
Because Vector is synchronized. Synchronization reduces the performance.
138 Q What is the security mechnaism used in java?
Java uses sand box security model.
139 Q What is sandbox?
A sandbox is a security mechanism for safely running programs. The sandbox typically provides a tightly-controlled set of resources for guest programs to run in, such as scratch space on disk and memory.
140 Q What is phantom memory?
Phantom memory is the memory that does not exist in reality.
141 Q What is reflection?
Reflection is the process of finding out the different features of a class dynamically.
142 Q What are the differences between JIT and HotSpot?
The Hotspot VM is a collection of techniques, the most important of which is called adaptive optimization. The original JVMs interpreted byte codes one at a time. Second-generation JVMs added a JIT compiler, which compiles each method to native code upon first execution, then executes the native code. Thereafter, whenever the method is called, the native code is executed. The adaptive optimization technique used by Hotspot is a hybrid approach, one that combines byte code interpretation and run-time compilation to native code. Hotspot, unlike a regular JIT compiling VM, doesn't do "premature optimization"
143 Q What are the advantages and disadvantages of reference counting in garbage collection?
An advantage of this scheme is that it can run in small chunks of time closely linked with the execution of the program. These characteristic makes it particularly suitable for real-time environments where the program can't be interrupted for very long time. A disadvantage of reference counting is that it does not detect cycles. A cycle is two or more objects that refer to one another. Another disadvantage is the overhead of incrementing and decrementing the reference count each time. Because of these disadvantages, reference counting currently is out of favor.
144 Q How would you implement a thread pool?
The ThreadPool class is a generic implementation of a thread pool, which takes the following input Size of the pool to be constructed and name of the class which implements Runnable (which has a visible default constructor) and constructs a thread pool with active threads that are waiting for activation. once the threads have finished processing they come back and wait once again in the pool.
145 Q What is the difference between throw and throws clause?
throw is used to throw an exception manually, where as throws is used in the case of checked exceptions, to tell the compiler that we haven't handled the exception, so that the exception will be handled by the calling function.
146 Q What is JAR file?
A JAR file (short for Java Archive) is a ZIP file used to distribute a set of Java classes. It is used to store compiled Java classes and associated metadata that can constitute a program
147 Q What is a classloader?
A class loader is an object that is responsible for loading classes.
148 Q What is the difference between Comparable and Comparator ?
The Comparable is for natural ordering and Comparator is for custom ordering. But we can override the compareTo method of comparable interface to give a custom ordering.
149 Q What is the difference between List, Set and Map?
A Set is a collection that has no duplicate elements. A List is a collection that has an order associated with its elements. A map is a way of storing key/value pairs. The way of storing a Map is similar to two-column table.
150 Q What is the difference between Exception and Error ?
Error is unrecoverable.
Core Java Interview Questions Part-IV
91 Q What is java byte code?
Byte code is an sort of intermediate code. The byte code is processed by virtual machine.
92 Q What is method overloading?
Method overloading is the process of creating a new method with the same name and different signature.
93 Q What is method overriding?
Method overriding is the process of giving a new definition for an existing method in its child class.
94 Q What is finalize() ?
Finalize is a protected method in java. When the garbage collector is executes , it will first call finalize( ), and on the next garbage-collection it reclaim the objects memory. So finalize( ), gives you the chance to perform some cleanup operation at the time of garbage collection.
95 Q What is multi-threading?
Multi-threading is the scenario where more than one threads are running.
96 Q What is deadlock?
Deadlock is a situation when two threads are waiting on each other to release a resource. Each thread waiting for a resource which is held by the other waiting thread.
97 Q What is the difference between Iterator and Enumeration?
Iterator differ from enumeration in two ways Iterator allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics. And , method names have been improved.
98 Q What is the Locale class?
A Locale object represents a specific geographical, political, or cultural region
99 Q What is internationalization?
Internationalization is the process of designing an application so that it can be adapted to various languages and regions without changes.
100 Q What is anonymous class ?
A An anonymous class is a type of inner class that don't have any name.
101 Q What is the difference between URL and URLConnection?
A URL represents the location of a resource, and a URLConnection represents a link for accessing or communicating with the resource at the location.
102 Q What are the two important TCP Socket classes?
ServerSocket and Socket. ServerSocket is useful for two-way socket communication. Socket class help us to read and write through the sockets. getInputStream() and getOutputStream() are the two methods available in Socket class.
103 Q Strings are immutable. But String s="Hello"; String s1=s+"World" returns HelloWorld how ?
Here actually a new object is created with the value of HelloWorld
104 Q What is classpath?
Classpath is the path where Java looks for loading class at run time and compile time.
105 Q What is path?
It is an the location where the OS will look for finding out the executable files and commands.
106 Q What is java collections?
Java collections is a set of classes, that allows operations on a collection of classes.
107 Q Can we compile a java program without main?
Yes, we can. In order to compile a java program, we don't require any main method. But to execute a java program we must have a main in it (unless it is an applet or servlet). Because main is the starting point of a java program.
108 Q What is a java compilation unit.
A compilation unit is a java source file.
109 What are the restrictions when overriding a method ?
Overridden methods must have the same name, argument list, and return type (i.e., they must have the exact signature of the method we are going to override, including return type.) The overriding method cannot be less visible than the method it overrides( i.e., a public method cannot be override to private). The overriding method may not throw any exceptions that may not be thrown by the overridden method
110 Q What is static initializer block? What is its use?
A static initializer block is a block of code that declares with the static keyword. It normally contains the block of code that must execute at the time of class loading. The static initializer block will execute only once at the time of loading the class only.
Byte code is an sort of intermediate code. The byte code is processed by virtual machine.
92 Q What is method overloading?
Method overloading is the process of creating a new method with the same name and different signature.
93 Q What is method overriding?
Method overriding is the process of giving a new definition for an existing method in its child class.
94 Q What is finalize() ?
Finalize is a protected method in java. When the garbage collector is executes , it will first call finalize( ), and on the next garbage-collection it reclaim the objects memory. So finalize( ), gives you the chance to perform some cleanup operation at the time of garbage collection.
95 Q What is multi-threading?
Multi-threading is the scenario where more than one threads are running.
96 Q What is deadlock?
Deadlock is a situation when two threads are waiting on each other to release a resource. Each thread waiting for a resource which is held by the other waiting thread.
97 Q What is the difference between Iterator and Enumeration?
Iterator differ from enumeration in two ways Iterator allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics. And , method names have been improved.
98 Q What is the Locale class?
A Locale object represents a specific geographical, political, or cultural region
99 Q What is internationalization?
Internationalization is the process of designing an application so that it can be adapted to various languages and regions without changes.
100 Q What is anonymous class ?
A An anonymous class is a type of inner class that don't have any name.
101 Q What is the difference between URL and URLConnection?
A URL represents the location of a resource, and a URLConnection represents a link for accessing or communicating with the resource at the location.
102 Q What are the two important TCP Socket classes?
ServerSocket and Socket. ServerSocket is useful for two-way socket communication. Socket class help us to read and write through the sockets. getInputStream() and getOutputStream() are the two methods available in Socket class.
103 Q Strings are immutable. But String s="Hello"; String s1=s+"World" returns HelloWorld how ?
Here actually a new object is created with the value of HelloWorld
104 Q What is classpath?
Classpath is the path where Java looks for loading class at run time and compile time.
105 Q What is path?
It is an the location where the OS will look for finding out the executable files and commands.
106 Q What is java collections?
Java collections is a set of classes, that allows operations on a collection of classes.
107 Q Can we compile a java program without main?
Yes, we can. In order to compile a java program, we don't require any main method. But to execute a java program we must have a main in it (unless it is an applet or servlet). Because main is the starting point of a java program.
108 Q What is a java compilation unit.
A compilation unit is a java source file.
109 What are the restrictions when overriding a method ?
Overridden methods must have the same name, argument list, and return type (i.e., they must have the exact signature of the method we are going to override, including return type.) The overriding method cannot be less visible than the method it overrides( i.e., a public method cannot be override to private). The overriding method may not throw any exceptions that may not be thrown by the overridden method
110 Q What is static initializer block? What is its use?
A static initializer block is a block of code that declares with the static keyword. It normally contains the block of code that must execute at the time of class loading. The static initializer block will execute only once at the time of loading the class only.
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