1. DATA STRUCTURES
1. What is data structure?
A data structure is a way of organizing data that considers not only the items stored, but
also their relationship to each other. Advance knowledge about the relationship between
data items allows designing of efficient algorithms for the manipulation of data.
2. List out the areas in which data structures are applied extensively?
1. Compiler Design,
2. Operating System,
3. Database Management System,
4. Statistical analysis package,
5. Numerical Analysis,
6. Graphics,
7. Artificial Intelligence,
8. Simulation
3. What are the major data structures used in the following areas : RDBMS,
Network data model and Hierarchical data model.
1. RDBMS = Array (i.e. Array of structures)
2. Network data model = Graph
3. Hierarchical data model = Trees
4. If you are using C language to implement the heterogeneous linked list, what
pointer type will you use?
The heterogeneous linked list contains different data types in its nodes and we need a
link, pointer to connect them. It is not possible to use ordinary pointers for this. So we go
for void pointer. Void pointer is capable of storing pointer to any type as it is a generic
pointer type.
5. Minimum number of queues needed to implement the priority queue?
Two. One queue is used for actual storing of data and another for storing priorities.
6. What is the data structures used to perform recursion?
Stack. Because of its LIFO (Last In First Out) property it remembers its 'caller' so knows
whom to return when the function has to return. Recursion makes use of system stack for
storing the return addresses of the function calls.
Every recursive function has its equivalent iterative (non-recursive) function. Even when
such equivalent iterative procedures are written, explicit stack is to be used.

2. 7. What are the notations used in Evaluation of Arithmetic Expressions using prefix
and postfix forms?
Polish and Reverse Polish notations.
8. Convert the expression ((A + B) * C - (D - E) ^ (F + G)) to equivalent Prefix and
Postfix notations.
1. Prefix Notation: ^ - * +ABC - DE + FG
2. Postfix Notation: AB + C * DE - - FG + ^
9. Sorting is not possible by using which of the following methods? (Insertion,
Selection, Exchange, Deletion)
Sorting is not possible in Deletion. Using insertion we can perform insertion sort, using
selection we can perform selection sort, using exchange we can perform the bubble sort
(and other similar sorting methods). But no sorting method can be done just using
deletion.
10. What are the methods available in storing sequential files ?
1. Straight merging,
2. Natural merging,
3. Polyphase sort,
4. Distribution of Initial runs.
11. List out few of the Application of tree data-structure?
1. The manipulation of Arithmetic expression,
2. Symbol Table construction,
3. Syntax analysis.
12. List out few of the applications that make use of Multilinked Structures?
1. Sparse matrix,
2. Index generation.
13. In tree construction which is the suitable efficient data structure? (Array,
Linked list, Stack, Queue)
Linked list is the suitable efficient data structure.
14. What is the type of the algorithm used in solving the 8 Queens problem?
Backtracking.

3. 15. In an AVL tree, at what condition the balancing is to be done?
If the 'pivotal value' (or the 'Height factor') is greater than 1 or less than -1.
16. What is the bucket size, when the overlapping and collision occur at same time?
One. If there is only one entry possible in the bucket, when the collision occurs, there is
no way to accommodate the colliding value. This results in the overlapping of values.
17. Classify the Hashing Functions based on the various methods by which the key
value is found.
1. Direct method,
2. Subtraction method,
3. Modulo-Division method,
4. Digit-Extraction method,
5. Mid-Square method,
6. Folding method,
7. Pseudo-random method.
18. What are the types of Collision Resolution Techniques and the methods used in
each of the type?
1. Open addressing (closed hashing), The methods used include: Overflow block.
2. Closed addressing (open hashing), The methods used include: Linked list,
Binary tree.
19. In RDBMS, what is the efficient data structure used in the internal storage
representation?
B+ tree. Because in B+ tree, all the data is stored only in leaf nodes, that makes searching
easier. This corresponds to the records that shall be stored in leaf nodes.
20. What is a spanning Tree?
A spanning tree is a tree associated with a network. All the nodes of the graph appear on
the tree once. A minimum spanning tree is a spanning tree organized so that the total
edge weight between nodes is minimized.
21. Does the minimum spanning tree of a graph give the shortest distance between
any 2 specified nodes?
No. The Minimal spanning tree assures that the total weight of the tree is kept at its
minimum. But it doesn't mean that the distance between any two nodes involved in the
minimum-spanning tree is minimum.

4. 22. Which is the simplest file structure? (Sequential, Indexed, Random)
Sequential is the simplest file structure.
23. Whether Linked List is linear or Non-linear data structure?
According to Access strategies Linked list is a linear one.
According to Storage Linked List is a Non-linear one.
DATA BASE MANAGEMENT SYSTEM
1. What is database?
A database is a logically coherent collection of data with some inherent meaning,
representing some aspect of real world and which is designed, built and populated with
data for a specific purpose.
2. What is DBMS?
It is a collection of programs that enables user to create and maintain a database. In other
words it is general-purpose software that provides the users with the processes of
defining, constructing and manipulating the database for various applications.
3. What is a Database system?
The database and DBMS software together is called as Database system.
4. What are the advantages of DBMS?
1. Redundancy is controlled.
2. Unauthorised access is restricted.
3. Providing multiple user interfaces.
4. Enforcing integrity constraints.
5. Providing backup and recovery.
5. What are the disadvantage in File Processing System?
1. Data redundancy and inconsistency.
2. Difficult in accessing data.
3. Data isolation.
4. Data integrity.
5. Concurrent access is not possible.
6. Security Problems.

5. 6. Describe the three levels of data abstraction?
The are three levels of abstraction:
1. Physical level: The lowest level of abstraction describes how data are stored.
2. Logical level: The next higher level of abstraction, describes what data are stored
in database and what relationship among those data.
3. View level: The highest level of abstraction describes only part of entire database.
7. Define the "integrity rules"?
There are two Integrity rules.
1. Entity Integrity: States that "Primary key cannot have NULL value"
2. Referential Integrity: States that "Foreign Key can be either a NULL value or
should be Primary Key value of other relation.
8. What is extension and intension?
1. Extension: It is the number of tuples present in a table at any instance. This is
time dependent.
2. Intension: It is a constant value that gives the name, structure of table and the
constraints laid on it.
9. What is System R? What are its two major subsystems?
System R was designed and developed over a period of 1974-79 at IBM San Jose
Research Center. It is a prototype and its purpose was to demonstrate that it is possible to
build a Relational System that can be used in a real life environment to solve real life
problems, with performance at least comparable to that of existing system.
Its two subsystems are
1. Research Storage
2. System Relational Data System.
10. How is the data structure of System R different from the relational structure?
Unlike Relational systems in System R
1. Domains are not supported
2. Enforcement of candidate key uniqueness is optional
3. Enforcement of entity integrity is optional
4. Referential integrity is not enforced

6. 11. What is Data Independence?
Data independence means that "the application is independent of the storage structure and
access strategy of data". In other words, The ability to modify the schema definition in
one level should not affect the schema definition in the next higher level.
Two types of Data Independence:
1. Physical Data Independence: Modification in physical level should not affect
the logical level.
2. Logical Data Independence: Modification in logical level should affect the view
level.
NOTE: Logical Data Independence is more difficult to achieve
12. What is a view? How it is related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist in its
own right but is instead derived from one or more underlying base table. In other words,
there is no stored file that direct represents the view instead a definition of view is stored
in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can
insulate users from the effects of restructuring and growth in the database. Hence
accounts for logical data independence.
13. What is Data Model?
A collection of conceptual tools for describing data, data relationships data semantics and
constraints.
14. What is E-R model?
This data model is based on real world that consists of basic objects called entities and of
relationship among these objects. Entities are described in a database by a set of
attributes.
15. What is Object Oriented model?
This model is based on collection of objects. An object contains values stored in instance
variables with in the object. An object also contains bodies of code that operate on the
object. These bodies of code are called methods. Objects that contain same types of
values and the same methods are grouped together into classes.
16. What is an Entity?
It is a 'thing' in the real world with an independent existence.

7. 17. What is an Entity type?
It is a collection (set) of entities that have same attributes.
18. What is an Entity set?
It is a collection of all entities of particular entity type in the database.
19. What is an Extension of entity type?
The collections of entities of a particular entity type are grouped together into an entity
set.
20. What is Weak Entity set?
An entity set may not have sufficient attributes to form a primary key, and its primary
key compromises of its partial key and primary key of its parent entity, then it is said to
be Weak Entity set.
21. What is an attribute?
It is a particular property, which describes the entity.
22. What is a Relation Schema and a Relation?
A relation Schema denoted by R(A1, A2, ..., An) is made up of the relation name R and
the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the
relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-
values t=(v1,v2, ..., vn).
23. What is degree of a Relation?
It is the number of attribute of its relation schema.
24. What is Relationship?
It is an association among two or more entities.
25. What is Relationship set?
The collection (or set) of similar relationships.
26. What is Relationship type?
Relationship type defines a set of associations or a relationship set among a given set of
entity types.

8. 27. What is degree of Relationship type?
It is the number of entity type participating.
28. What is DDL (Data Definition Language)?
A data base schema is specifies by a set of definitions expressed by a special language
called DDL.
29. What is VDL (View Definition Language)?
It specifies user views and their mappings to the conceptual schema.
30. What is SDL (Storage Definition Language)?
This language is to specify the internal schema. This language may specify the mapping
between two schemas.
31. What is Data Storage - Definition Language?
The storage structures and access methods used by database system are specified by a set
of definition in a special type of DDL called data storage-definition language.
32. What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data as organised by appropriate
data model.
1. Procedural DML or Low level: DML requires a user to specify what data are
needed and how to get those data.
2. Non-Procedural DML or High level: DML requires a user to specify what data
are needed without specifying how to get those data.
33. What is DML Compiler?
It translates DML statements in a query language into low-level instruction that the query
evaluation engine can understand.
34. What is Query evaluation engine?
It executes low-level instruction generated by compiler.
35. What is DDL Interpreter?
It interprets DDL statements and record them in tables containing metadata.

9. 36. What is Record-at-a-time?
The Low level or Procedural DML can specify and retrieve each record from a set of
records. This retrieve of a record is said to be Record-at-a-time.
37. What is Set-at-a-time or Set-oriented?
The High level or Non-procedural DML can specify and retrieve many records in a single
DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.
38. What is Relational Algebra?
It is procedural query language. It consists of a set of operations that take one or two
relations as input and produce a new relation.
39. What is Relational Calculus?
It is an applied predicate calculus specifically tailored for relational databases proposed
by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.
40. How does Tuple-oriented relational calculus differ from domain-oriented
relational calculus?
1. The tuple-oriented calculus uses a tuple variables i.e., variable whose only
permitted values are tuples of that relation. E.g. QUEL
2. The domain-oriented calculus has domain variables i.e., variables that range
over the underlying domains instead of over relation. E.g. ILL, DEDUCE.
41. What is normalization?
It is a process of analysing the given relation schemas based on their Functional
Dependencies (FDs) and primary key to achieve the properties
(1).Minimizing redundancy, (2). Minimizing insertion, deletion and update anomalies.
42. What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that
are subsets of R specifies a constraint on the possible tuple that can form a relation state r
of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have
t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the
value of component Y.
43. What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation
schemas after decomposition.

10. 44. What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.
45. What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full
functional dependency if removal of any attribute A from X means that the dependency
does not hold any more.
46. What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully
functionally dependent on primary key.
47. What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the
following is true
1. X is a Super-key of R.
2. A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.
48. What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that
for every FD X A, X must be a candidate key.
49. What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that
holds over R, one of following is true.
1.) X is subset or equal to (or) XY = R.
2.) X is a super key.
50. What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that
holds R, one the following is true 1.) Ri = R for some i.
2.) The join dependency is implied by the set of FD, over R in which the left side is key
of R.
51. What is Domain-Key Normal Form?

11. A relation is said to be in DKNF if all constraints and dependencies that should hold on
the the constraint can be enforced by simply enforcing the domain constraint and key
constraint on the relation.
52. What are partial, alternate,, artificial, compound and natural key?
1. Partial Key: It is a set of attributes that can uniquely identify weak entities and
that are related to same owner entity. It is sometime called as Discriminator.
2. Alternate Key: All Candidate Keys excluding the Primary Key are known as
Alternate Keys.
3. Artificial Key: If no obvious key, either stand alone or compound is available,
then the last resort is to simply create a key, by assigning a unique number to each
record or occurrence. Then this is known as developing an artificial key.
4. Compound Key: If no single data element uniquely identifies occurrences within
a construct, then combining multiple elements to create a unique identifier for the
construct is known as creating a compound key.
5. Natural Key: When one of the data elements stored within a construct is utilized
as the primary key, then it is called the natural key.
53. What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
1. Binary search style indexing
2. B-Tree indexing
3. Inverted list indexing
4. Memory resident table
5. Table indexing
54. What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about
every relation and index that it contains. This information is stored in a collection of
relations maintained by the system called metadata. It is also called data dictionary.
55. What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has the
least estimated cost is referred to as query optimization.
56. What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its effects
should persist even if the system crashes before all its changes are reflected on disk. This
property is called durability.

12. 57. What do you mean by atomicity and aggregation?
1. Atomicity: Either all actions are carried out or none are. Users should not have to
worry about the effect of incomplete transactions. DBMS ensures this by undoing
the actions of incomplete transactions.
2. Aggregation: A concept which is used to model a relationship between a
collection of entities and relationships. It is used when we need to express a
relationship among relationships.
58. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause
the deadlock detection algorithms to identify deadlocks that do not really exist. Such
situations are called phantom deadlocks and they lead to unnecessary aborts.
59. What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS
can reduce the amount of work to be done during restart in the event of subsequent
crashes.
60. What are the different phases of transaction?
Different phases are
1.) Analysis phase,
2.) Redo Phase,
3.) Undo phase.
61. What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no cross-
file capabilities but is user-friendly and provides user-interface management.
62. What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from user.
63. What is a query?
A query with respect to DBMS relates to user commands that are used to interact with a
data base. The query language can be classified into data definition language and data
manipulation language.

13. 64. What do you mean by Correlated subquery?
Subqueries, or nested queries, are used to bring back a set of rows to be used by
the parent query. Depending on how the subquery is written, it can be executed once for
the parent query or it can be executed once for each row returned by the parent query. If
the subquery is executed for each row of the parent, this is called a correlated subquery.
A correlated subquery can be easily identified if it contains any references to the
parent subquery columns in its WHERE clause. Columns from the subquery cannot be
referenced anywhere else in the parent query. The following example demonstrates a
non-correlated subquery.
Example: Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER
Where CUST.CNUM = ORDER.CNUM)
65. What are the primitive operations common to all record management systems?
Addition, deletion and modification.
66. Name the buffer in which all the commands that are typed in are stored?
'Edit' Buffer.
67. What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
68. Are the resulting relations of PRODUCT and JOIN operation the same?
No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
69. What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software, and
the data dictionary, which consists of the system-level data structures used by the kernel
to manage the database You might think of an RDBMS as an operating system (or set of
subsystems), designed specifically for controlling data access; its primary functions are
storing, retrieving, and securing data. An RDBMS maintains its own list of authorized
users and their associated privileges; manages memory caches and paging; controls
locking for concurrent resource usage; dispatches and schedules user requests; and
manages space usage within its table-space structures.

14. 70. Name the sub-systems of a RDBMS.
I/O, Security, Language Processing, Process Control, Storage Management, Logging and
Recovery, Distribution Control, Transaction Control, Memory Management, Lock
Management.
71. Which part of the RDBMS takes care of the data dictionary? How?
Data dictionary is a set of tables and database objects that is stored in a special area of the
database and maintained exclusively by the kernel.
72. What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides
access to them, and maps the actual physical storage location.
73. How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL).
74. Define SQL and state the differences between SQL and other conventional
programming Languages.
SQL is a nonprocedural language that is designed specifically for data access operations
on normalized relational database structures. The primary difference between SQL and
other conventional programming languages is that SQL statements specify what data
operations should be performed rather than how to perform them.
75. Name the three major set of files on disk that compose a database in Oracle.
There are three major sets of files on disk that compose a database. All the files are
binary. These are
1.) Database files
2.) Control files
3.) Redo logs
The most important of these are the database files where the actual data resides. The
control files and the redo logs support the functioning of the architecture itself. All three
sets of files must be present, open, and available to Oracle for any data on the database to
be useable. Without these files, you cannot access the database, and the database
administrator might have to recover some or all of the database using a backup, if there is
one.
76. What is database Trigger?

15. A database trigger is a PL/SQL block that can defined to automatically execute for insert,
update, and delete statements against a table. The trigger can e defined to execute once
for the entire statement or once for every row that is inserted, updated, or deleted. For any
one table, there are twelve events for which you can define database triggers. A database
trigger can call database procedures that are also written in PL/SQL.
77. What are stored-procedures? And what are the advantages of using them?
Stored procedures are database objects that perform a user defined operation. A stored
procedure can have a set of compound SQL statements. A stored procedure executes the
SQL commands and returns the result to the client. Stored procedures are used to reduce
network traffic.
78. What is Storage Manager?
It is a program module that provides the interface between the low-level data stored in
database, application programs and queries submitted to the system
79. What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into main
memory and deciding what data to be cache in memory.
80. What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state despite
system failures and concurrent transaction execution proceeds without conflicting.
81. What is File Manager?
It is a program module, which manages the allocation of space on disk storage and data
structure used to represent information stored on a disk.
82. What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and
checks the authority of user to access data.
83. What are stand-alone procedures?
Procedures that are not part of a package are known as stand-alone because they
independently defined. A good example of a stand-alone procedure is one written in a
SQL*Forms application. These types of procedures are not available for reference from
other Oracle tools. Another limitation of stand-alone procedures is that they are compiled
at run time, which slows execution.

16. 84. What are cursors give different types of cursors?
PL/SQL uses cursors for all database information accesses statements. The language
supports the use two types of cursors
1.) Implicit
2.) Explicit
85. What is cold backup and hot backup (in case of Oracle)?
1. Cold Backup: It is copying the three sets of files (database files, redo logs, and
control file) when the instance is shut down. This is a straight file copy, usually
from the disk directly to tape. You must shut down the instance to guarantee a
consistent copy. If a cold backup is performed, the only option available in the
event of data file loss is restoring all the files from the latest backup. All work
performed on the database since the last backup is lost.
2. Hot Backup: Some sites (such as worldwide airline reservations systems) cannot
shut down the database while making a backup copy of the files. The cold backup
is not an available option.
86. What is meant by Proactive, Retroactive and Simultaneous Update.
1. Proactive Update: The updates that are applied to database before it becomes
effective in real world.
2. Retroactive Update: The updates that are applied to database after it becomes
effective in real world.
3. Simulatneous Update: The updates that are applied to database at the same time
when it becomes effective in real world.
CORE JAVA
1. What is the most important feature of Java?
Java is a platform independent language.
2. What do you mean by platform independence?
Platform independence means that we can write and compile the java code in one
platform (eg Windows) and can execute the class in any other supported platform eg
(Linux,Solaris,etc).
3. What is a JVM?
JVM is Java Virtual Machine which is a run time environment for the compiled java class
files.
4. Are JVM's platform independent?

17. JVM's are not platform independent. JVM's are platform specific run time
implementation provided by the vendor.
5. What is the difference between a JDK and a JVM?
JDK is Java Development Kit which is for development purpose and it includes
execution environment also. But JVM is purely a run time environment and hence you
will not be able to compile your source files using a JVM.
6. What is a pointer and does Java support pointers?
Pointer is a reference handle to a memory location. Improper handling of pointers leads
to memory leaks and reliability issues hence Java doesn't support the usage of pointers.
7. What is the base class of all classes?
java.lang.Object
8. Does Java support multiple inheritance?
Java doesn't support multiple inheritance.
9. Is Java a pure object oriented language?
Java uses primitive data types and hence is not a pure object oriented language.
10. Are arrays primitive data types?
In Java, Arrays are objects.
11. What is difference between Path and Classpath?
Path and Classpath are operating system level environment variales. Path is used define
where the system can find the executables(.exe) files and classpath is used to specify the
location .class files.
12. What are local variables?
Local varaiables are those which are declared within a block of code like methods. Local
variables should be initialised before accessing them.
13. What are instance variables?
Instance variables are those which are defined at the class level. Instance variables need
not be initialized before using them as they are automatically initialized to their default
values.

18. 14. How to define a constant variable in Java?
The variable should be declared as static and final. So only one copy of the variable
exists for all instances of the class and the value can't be changed also.
static final int PI = 2.14; is an example for constant.
15. Should a main() method be compulsorily declared in all java classes?
No not required. main() method should be defined only if the source class is a java
application.
16. What is the return type of the main() method?
Main() method doesn't return anything hence declared void.
17. Why is the main() method declared static?
main() method is called by the JVM even before the instantiation of the class hence it is
declared as static.
18. What is the arguement of main() method?
main() method accepts an array of String object as arguement.
19. Can a main() method be overloaded?
Yes. You can have any number of main() methods with different method signature and
implementation in the class.
20. Can a main() method be declared final?
Yes. Any inheriting class will not be able to have it's own default main() method.
21. Does the order of public and static declaration matter in main() method?
No. It doesn't matter but void should always come before main().
22. Can a source file contain more than one class declaration?
Yes a single source file can contain any number of Class declarations but only one of the
class can be declared as public.
23. What is a package?
Package is a collection of related classes and interfaces. package declaration should be
first statement in a java class.

19. 24. Which package is imported by default?
java.lang package is imported by default even without a package declaration.
25. Can a class declared as private be accessed outside it's package?
Not possible.
26. Can a class be declared as protected?
A class can't be declared as protected. only methods can be declared as protected.
27. What is the access scope of a protected method?
A protected method can be accessed by the classes within the same package or by the
subclasses of the class in any package.
28. What is the purpose of declaring a variable as final?
A final variable's value can't be changed. final variables should be initialized before using
them.
29. What is the impact of declaring a method as final?
A method declared as final can't be overridden. A sub-class can't have the same method
signature with a different implementation.
30. I don't want my class to be inherited by any other class. What should i do?
You should declared your class as final. But you can't define your class as final, if it is an
abstract class. A class declared as final can't be extended by any other class.
31. Can you give few examples of final classes defined in Java API?
java.lang.String, java.lang.Math are final classes.
32. How is final different from finally and finalize()?
final is a modifier which can be applied to a class or a method or a variable. final class
can't be inherited, final method can't be overridden and final variable can't be changed.
finally is an exception handling code section which gets executed whether an exception is
raised or not by the try block code segment.
finalize() is a method of Object class which will be executed by the JVM just before
garbage collecting object to give a final chance for resource releasing activity.

20. 33. Can a class be declared as static?
No a class cannot be defined as static. Only a method, a variable or a block of code can
be declared as static.
34. When will you define a method as static?
When a method needs to be accessed even before the creation of the object of the class
then we should declare the method as static.
35. What are the restriction imposed on a static method or a static block of code?
A static method should not refer to instance variables without creating an instance and
cannot use "this" operator to refer the instance.
36. I want to print "Hello" even before main() is executed. How will you acheive
that?
Print the statement inside a static block of code. Static blocks get executed when the class
gets loaded into the memory and even before the creation of an object. Hence it will be
executed before the main() method. And it will be executed only once.
37. What is the importance of static variable?
static variables are class level variables where all objects of the class refer to the same
variable. If one object changes the value then the change gets reflected in all the objects.
38. Can we declare a static variable inside a method?
Static varaibles are class level variables and they can't be declared inside a method. If
declared, the class will not compile.
39. What is an Abstract Class and what is it's purpose?
A Class which doesn't provide complete implementation is defined as an abstract class.
Abstract classes enforce abstraction.
40. Can a abstract class be declared final?
Not possible. An abstract class without being inherited is of no use and hence will result
in compile time error.
41. What is use of a abstract variable?
Variables can't be declared as abstract. only classes and methods can be declared as
abstract.

21. 42. Can you create an object of an abstract class?
Not possible. Abstract classes can't be instantiated
43. Can a abstract class be defined without any abstract methods?
Yes it's possible. This is basically to avoid instance creation of the class.
44. Class C implements Interface I containing method m1 and m2 declarations.
Class C has provided implementation for method m2. Can i create an object of
Class C?
No not possible. Class C should provide implementation for all the methods in the
Interface I. Since Class C didn't provide implementation for m1 method, it has to be
declared as abstract. Abstract classes can't be instantiated.
45. Can a method inside a Interface be declared as final?
No not possible. Doing so will result in compilation error. public and abstract are the only
applicable modifiers for method declaration in an interface.
46. Can an Interface implement another Interface?
Intefaces doesn't provide implementation hence a interface cannot implement another
interface.
47. Can an Interface extend another Interface?
Yes an Interface can inherit another Interface, for that matter an Interface can extend
more than one Interface.
48. Can a Class extend more than one Class?
Not possible. A Class can extend only one class but can implement any number of
Interfaces.
49. Why is an Interface be able to extend more than one Interface but a Class can't
extend more than one Class?
Basically Java doesn't allow multiple inheritance, so a Class is restricted to extend only
one Class. But an Interface is a pure abstraction model and doesn't have inheritance
hierarchy like classes(do remember that the base class of all classes is Object). So an
Interface is allowed to extend more than one Interface.
50. Can an Interface be final?

22. Not possible. Doing so so will result in compilation error.
51. Can a class be defined inside an Interface?
Yes it's possible.
52. Can an Interface be defined inside a class?
Yes it's possible.
53. What is a Marker Interface?
An Interface which doesn't have any declaration inside but still enforces a mechanism.
54. Which object oriented Concept is achieved by using overloading and overriding?
Polymorphism.
55. Why does Java not support operator overloading?
Operator overloading makes the code very difficult to read and maintain. To maintain
code simplicity, Java doesn't support operator overloading.
56. Can we define private and protected modifiers for variables in interfaces?
No.
57. What is Externalizable?
Externalizable is an Interface that extends Serializable Interface. And sends data into
Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and
readExternal(ObjectInput in)
58. What modifiers are allowed for methods in an Interface?
Only public and abstract modifiers are allowed for methods in interfaces.
59. What is a local, member and a class variable?
Variables declared within a method are "local" variables.
Variables declared within the class i.e not within any methods are "member" variables
(global variables).

23. Variables declared within the class i.e not within any methods and are defined as "static"
are class variables.
60. What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.
61. What value does read() return when it has reached the end of a file?
The read() method returns -1 when it has reached the end of a file.
62. Can a Byte object be cast to a double value?
No, an object cannot be cast to a primitive value.
63. What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of
the class's outer class. A static inner class does not have any object instances.
64. What is an object's lock and which object's have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized
access to the object. A thread may execute a synchronized method of an object only after
it has acquired the object's lock. All objects and classes have locks. A class's lock is
acquired on the class's Class object.
65. What is the % operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing
the first operand by the second operand.
66. When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the
referenced interface.
67. Which class is extended by all other classes?
The Object class is extended by all other classes.
68. Which non-Unicode letter characters may be used as the first character of an
identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an
identifier

24. 69. What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
70. What is casting?
There are two types of casting, casting between primitive numeric types and casting
between object references. Casting between numeric types is used to convert larger
values, such as double values, to smaller values, such as byte values. Casting between
object references is used to refer to an object by a compatible class, interface, or array
type reference.
71. What is the return type of a program's main() method?
void.
72. If a variable is declared as private, where may the variable be accessed?
A private variable may only be accessed within the class in which it is declared.
73. What do you understand by private, protected and public?
These are accessibility modifiers. Private is the most restrictive, while public is the least
restrictive. There is no real difference between protected and the default type (also known
as package protected) within the context of the same package, however the protected
keyword allows visibility to a derived class in a different package.
74. What is Downcasting ?
Downcasting is the casting from a general to a more specific type, i.e. casting down the
hierarchy
75. What modifiers may be used with an inner class that is a member of an outer
class?
A (non-local) inner class may be declared as public, protected, private, static, final, or
abstract.
76. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8
characters?
Unicode requires 16 bits and ASCII require 7 bits Although the ASCII character set uses
only 7 bits, it is usually represented as 8 bits.
UTF-8 represents characters using 8, 16, and 18 bit patterns.

25. UTF-16 uses 16-bit and larger bit patterns.
77. What restrictions are placed on the location of a package statement within a
source code file?
A package statement must appear as the first line in a source code file (excluding blank
lines and comments).
78. What is a native method?
A native method is a method that is implemented in a language other than Java.
79. What are order of precedence and associativity, and how are they used?
Order of precedence determines the order in which operators are evaluated in
expressions. Associatity determines whether an expression is evaluated left-to-right or
right-to-left.
80. Can an anonymous class be declared as implementing an interface and
extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be
declared to do both.
81. What is the range of the char type?
The range of the char type is 0 to 216 - 1 (i.e. 0 to 65535.)
82. What is the range of the short type?
The range of the short type is -(215) to 215 - 1. (i.e. -32,768 to 32,767)
83. Why isn't there operator overloading?
Because C++ has proven by example that operator overloading makes code almost
impossible to maintain.
84. What does it mean that a method or field is "static"?
Static variables and methods are instantiated only once per class. In other words they are
class variables, not instance variables. If you change the value of a static variable in a
particular object, the value of that variable changes for all instances of that class. Static
methods can be referenced with the name of the class rather than the name of a particular
object of the class (though that works too). That's how library methods like
System.out.println() work. out is a static field in the java.lang.System class.

26. 85. Is null a keyword?
The null value is not a keyword.
86. Which characters may be used as the second character of an identifier, but not
as the first character of an identifier?
The digits 0 through 9 may not be used as the first character of an identifier but they may
be used after the first character of an identifier.
87. Is the ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.
88. How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.
89. If a class is declared without any access modifiers, where may the class be
accessed?
A class that is declared without any access modifiers is said to have package access. This
means that the class can only be accessed by other classes and interfaces that are defined
within the same package.
90. Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.
91. Name the eight primitive Java types.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.
92. What restrictions are placed on the values of each case of a switch statement?
During compilation, the values of each case of a switch statement must evaluate to a
value that can be promoted to an int value.
93. What is the difference between a while statement and a do while statement?
A while statement checks at the beginning of a loop to see whether the next loop iteration
should occur. A do while statement checks at the end of a loop to see whether the next
iteration of a loop should occur. The do whilestatement will always execute the body of a
loop at least once.
94. What modifiers can be used with a local inner class?

27. A local inner class may be final or abstract.
95. When does the compiler supply a default constructor for a class?
The compiler supplies a default constructor for a class if no other constructors are
provided.
96. If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or
by subclasses of the class in which it is declared.
97. What are the legal operands of the instanceof operator?
The left operand is an object reference or null value and the right operand is a class,
interface, or array type.
98. Are true and false keywords?
The values true and false are not keywords.
99. What happens when you add a double value to a String?
The result is a String object.
100. What is the diffrence between inner class and nested class?
When a class is defined within a scope od another class, then it becomes inner class. If
the access modifier of the inner class is static, then it becomes nested class.
101. Can an abstract class be final?
An abstract class may not be declared as final.
102. What is numeric promotion?
Numeric promotion is the conversion of a smaller numeric type to a larger numeric type,
so that integer and floating-point operations may take place. In numerical promotion,
byte, char, and short values are converted to int values. The int values are also converted
to long values, if necessary. The long and float values are converted to double values, as
required.
103. What is the difference between a public and a non-public class?
A public class may be accessed outside of its package. A non-public class may not be
accessed outside of its package.

28. 104. To what value is a variable of the boolean type automatically initialized?
The default value of the boolean type is false.
105. What is the difference between the prefix and postfix forms of the ++ operator?
The prefix form performs the increment operation and returns the value of the increment
operation. The postfix form returns the current value all of the expression and then
performs the increment operation on that value.
106. What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The
overriding method may not limit the access of the method it overrides. The overriding
method may not throw any exceptions that may not be thrown by the overridden method.
107. What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to
create a separate name space for groups of classes and interfaces. Packages are also used
to organize related classes and interfaces into a single API unit and to control
accessibility to these classes and interfaces.
108. What modifiers may be used with a top-level class?
A top-level class may be public, abstract, or final.
109. What is the difference between an if statement and a switch statement?
The if statement is used to select among two alternatives. It uses a boolean expression to
decide which alternative should be executed. The switch statement is used to select
among multiple alternatives. It uses an int expression to determine which alternative
should be executed.
110. What are the practical benefits, if any, of importing a specific class rather than
an entire package (e.g. import java.net.* versus import java.net.Socket)?
It makes no difference in the generated class files since only the classes that are actually
used are referenced by the generated class file. There is another practical benefit to
importing single classes, and this arises when two (or more) packages have classes with
the same name. Take java.util.Timer and javax.swing.Timer, for example. If I import
java.util.* and javax.swing.* and then try to use "Timer", I get an error while compiling
(the class name is ambiguous between both packages). Let's say what you really wanted
was the javax.swing.Timer class, and the only classes you plan on using in java.util are
Collection and HashMap. In this case, some people will prefer to import
java.util.Collection and import java.util.HashMap instead of importing java.util.*. This

29. will now allow them to use Timer, Collection, HashMap, and other javax.swing classes
without using fully qualified class names in.
111. Can a method be overloaded based on different return type but same argument
type ?
No, because the methods can be called without using their return type in which case there
is ambiquity for the compiler.
112. What happens to a static variable that is defined within a method of a class ?
Can't do it. You'll get a compilation error.
113. How many static initializers can you have ?
As many as you want, but the static initializers and class variable initializers are executed
in textual order and may not refer to class variables declared in the class whose
declarations appear textually after the use, even though these class variables are in scope.
114. What is the difference between method overriding and overloading?
Overriding is a method with the same name and arguments as in a parent, whereas
overloading is the same method name but different arguments
115. What is constructor chaining and how is it achieved in Java ?
A child object constructor always first needs to construct its parent (which in turn calls its
parent constructor.). In Java it is done via an implicit call to the no-args constructor as the
first statement.
116. What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are
evaluated. Then the & operator is applied to the operand. When an expression involving
the && operator is evaluated, the first operand is evaluated. If the first operand returns a
value of true then the second operand is evaluated. The && operator is then applied to
the first and second operands. If the first operand evaluates to false, the evaluation of the
second operand is skipped.
117. Which Java operator is right associative?
The = operator is right associative.
118. Can a double value be cast to a byte?
Yes, a double value can be cast to a byte.

30. 119. What is the difference between a break statement and a continue statement?
A break statement results in the termination of the statement to which it applies (switch,
for, do, or while). A continue statement is used to end the current loop iteration and
return control to the loop statement.
120. Can a for statement loop indefinitely?
Yes, a for statement can loop indefinitely. For example, consider the following: for(;;);
121. To what value is a variable of the String type automatically initialized?
The default value of an String type is null.
122. What is the difference between a field variable and a local variable?
A field variable is a variable that is declared as a member of a class. A local variable is a
variable that is declared local to a method.
123. How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a
superclass constructor.
124. What does it mean that a class or member is final?
A final class cannot be inherited. A final method cannot be overridden in a subclass. A
final field cannot be changed after it's initialized, and it must include an initializer
statement where it's declared.
125. What does it mean that a method or class is abstract?
An abstract class cannot be instantiated. Abstract methods may only be included in
abstract classes. However, an abstract class is not required to have any abstract methods,
though most of them do. Each subclass of an abstract class must override the abstract
methods of its superclasses or it also should be declared abstract.
126. What is a transient variable?
Transient variable is a variable that may not be serialized.
127. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by
the operation.

31. 128. What is the difference between the >> and >>> operators?
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have
been shifted out.
129. Is sizeof a keyword?
The sizeof operator is not a keyword.
JAVA BASICS
1. What is the difference between a constructor and a method?
A constructor is a member function of a class that is used to create objects of that class. It
has the same name as the class itself, has no return type, and is invoked using the new
operator.
A method is an ordinary member function of a class. It has its own name, a return type
(which may be void), and is invoked using the dot operator.
2. What is the purpose of garbage collection in Java, and when is it used?
The purpose of garbage collection is to identify and discard objects that are no longer
needed by a program so that their resources can be reclaimed and reused.
A Java object is subject to garbage collection when it becomes unreachable to the
program in which it is used.
3. Describe synchronization in respect to multithreading.
With respect to multithreading, synchronization is the capability to control the access of
multiple threads to shared resources.
Without synchonization, it is possible for one thread to modify a shared variable while
another thread is in the process of using or updating same shared variable. This usually
leads to significant errors.
4. What is an abstract class?
Abstract class must be extended/subclassed (to be useful). It serves as a template. A class
that is abstract may not be instantiated (ie. you may not call its constructor), abstract class
may contain static data.
Any class with an abstract method is automatically abstract itself, and must be declared
as such. A class may be declared abstract even if it has no abstract methods. This
prevents it from being instantiated.

32. 5. What is the difference between an Interface and an Abstract class?
An abstract class can have instance methods that implement a default behavior. An
Interface can only declare constants and instance methods, but cannot implement default
behavior and all methods are implicitly abstract.
An interface has all public members and no implementation. An abstract class is a class
which may have the usual flavors of class members (private, protected, etc.), but has
some abstract methods.
6. Explain different way of using thread?
The thread could be implemented by using runnable interface or by inheriting from the
Thread class. The former is more advantageous, 'cause when you are going for multiple
inheritance, the only interface can help.
7. What is an Iterator?
Some of the collection classes provide traversal of their contents via a java.util.Iterator
interface. This interface allows you to walk through a collection of objects, operating on
each object in turn.
Remember when using Iterators that they contain a snapshot of the collection at the time
the Iterator was obtained; generally it is not advisable to modify the collection itself while
traversing an Iterator.
8. State the significance of public, private, protected, default modifiers both singly
and in combination and state the effect of package relationships on declared items
qualified by these modifiers.
public: Public class is visible in other packages, field is visible everywhere (class must be
public too)
private : Private variables or methods may be used only by an instance of the same class
that declares the variable or method, A private feature may only be accessed by the class
that owns the feature.
protected : Is available to all classes in the same package and also available to all
subclasses of the class that owns the protected feature. This access is provided even to
subclasses that reside in a different package from the class that owns the protected
feature.
What you get by default ie, without any access modifier (ie, public private or protected).
It means that it is visible to all within a particular package.
9. What is static in java?

33. Static means one per class, not one for each object no matter how many instance of a
class might exist. This means that you can use them without creating an instance of a
class.Static methods are implicitly final, because overriding is done based on the type of
the object, and static methods are attached to a class, not an object.
A static method in a superclass can be shadowed by another static method in a subclass,
as long as the original method was not declared final. However, you can't override a static
method with a nonstatic method. In other words, you can't change a static method into an
instance method in a subclass.
10. What is final class?
A final class can't be extended ie., final class may not be subclassed. A final method can't
be overridden when its class is inherited. You can't change value of a final variable (is a
constant).
11. What if the main() method is declared as private?
The program compiles properly but at runtime it will give "main() method not public."
message.
12. What if the static modifier is removed from the signature of the main() method?
Program compiles. But at runtime throws an error "NoSuchMethodError".
13. What if I write static public void instead of public static void?
Program compiles and runs properly.
14. What if I do not provide the String array as the argument to the method?
Program compiles but throws a runtime error "NoSuchMethodError".
15. What is the first argument of the String array in main() method?
The String array is empty. It does not have any element. This is unlike C/C++ where the
first element by default is the program name.
16. If I do not provide any arguments on the command line, then the String array of
main() method will be empty or null?
It is empty. But not null.
17. How can one prove that the array is not null but empty using one line of code?

34. Print args.length. It will print 0. That means it is empty. But if it would have been null
then it would have thrown a NullPointerException on attempting to print args.length.
18. What environment variables do I need to set on my machine in order to be able
to run Java programs?
CLASSPATH and PATH are the two variables.
19. Can an application have multiple classes having main() method?
Yes it is possible. While starting the application we mention the class name to be run.
The JVM will look for the Main method only in the class whose name you have
mentioned.
Hence there is not conflict amongst the multiple classes having main() method.
20. Can I have multiple main() methods in the same class?
No the program fails to compile. The compiler says that the main() method is already
defined in the class.
21. Do I need to import java.lang package any time? Why ?
No. It is by default loaded internally by the JVM.
22. Can I import same package/class twice? Will the JVM load the package twice at
runtime?
One can import the same package or same class multiple times. Neither compiler nor
JVM complains about it. And the JVM will internally load the class only once no matter
how many times you import the same class.
23. What are Checked and UnChecked Exception?
A checked exception is some subclass of Exception (or Exception itself), excluding class
RuntimeException and its subclasses. Making an exception checked forces client
programmers to deal with the possibility that the exception will be thrown.
Example: IOException thrown by java.io.FileInputStream's read() method·
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and
its subclasses also are unchecked. With an unchecked exception, however, the compiler
doesn't force client programmers either to catch the exception or declare it in a throws
clause. In fact, client programmers may not even know that the exception could be
thrown.

35. Example: StringIndexOutOfBoundsException thrown by String's charAt() method·
Checked exceptions must be caught at compile time. Runtime exceptions do not need to
be. Errors often cannot be.
24. What is Overriding?
When a class defines a method using the same name, return type, and arguments as a
method in its superclass, the method in the class overrides the method in the superclass.
When the method is invoked for an object of the class, it is the new definition of the
method that is called, and not the method definition from superclass. Methods may be
overridden to be more public, not more private.
25. Are the imports checked for validity at compile time? Example: will the code
containing an import such as java.lang.ABCD compile?
Yes the imports are checked for the semantic validity at compile time. The code
containing above line of import will not compile. It will throw an error saying, can not
resolve symbol
symbol : class ABCD
location: package io
import java.io.ABCD;
26. Does importing a package imports the subpackages as well? Example: Does
importing com.MyTest.* also import com.MyTest.UnitTests.*?
No you will have to import the subpackages explicitly. Importing com.MyTest.* will
import classes in the package MyTest only. It will not import any class in any of it's
subpackage.
27. What is the difference between declaring a variable and defining a variable?
In declaration we just mention the type of the variable and it's name. We do not initialize
it. But defining means declaration + initialization.
Example: String s; is just a declaration while String s = new String ("abcd"); Or String s
= "abcd"; are both definitions.
28. What is the default value of an object reference declared as an instance
variable?
The default value will be null unless we define it explicitly.

36. 29. Can a top level class be private or protected?
No. A top level class cannot be private or protected. It can have either "public" or no
modifier. If it does not have a modifier it is supposed to have a default access.
If a top level class is declared as private the compiler will complain that the "modifier
private is not allowed here". This means that a top level class can not be private. Same is
the case with protected.
30. What type of parameter passing does Java support?
In Java the arguments are always passed by value.
31. Primitive data types are passed by reference or pass by value?
Primitive data types are passed by value.
32. Objects are passed by value or by reference?
Java only supports pass by value. With objects, the object reference itself is passed by
value and so both the original reference and parameter copy both refer to the same object.
33. What is serialization?
Serialization is a mechanism by which you can save the state of an object by converting it
to a byte stream.
34. How do I serialize an object to a file?
The class whose instances are to be serialized should implement an interface Serializable.
Then you pass the instance to the ObjectOutputStream which is connected to a
fileoutputstream. This will save the object to a file.
35. Which methods of Serializable interface should I implement?
The serializable interface is an empty interface, it does not contain any methods. So we
do not implement any methods.
36. How can I customize the seralization process? i.e. how can one have a control
over the serialization process?
Yes it is possible to have control over serialization process. The class should implement
Externalizable interface. This interface contains two methods namely readExternal and
writeExternal.

37. You should implement these methods and write the logic for customizing the serialization
process.
37. What is the common usage of serialization?
Whenever an object is to be sent over the network, objects need to be serialized.
Moreover if the state of an object is to be saved, objects need to be serilazed.
38. What is Externalizable interface?
Externalizable is an interface which contains two methods readExternal and
writeExternal. These methods give you a control over the serialization mechanism.
Thus if your class implements this interface, you can customize the serialization process
by implementing these methods.
39. When you serialize an object, what happens to the object references included in
the object?
The serialization mechanism generates an object graph for serialization. Thus it
determines whether the included object references are serializable or not. This is a
recursive process.
Thus when an object is serialized, all the included objects are also serialized alongwith
the original obect.
40. What one should take care of while serializing the object?
One should make sure that all the included objects are also serializable. If any of the
objects is not serializable then it throws a NotSerializableException.
41. What happens to the static fields of a class during serialization?
There are three exceptions in which serialization doesnot necessarily read and write to the
stream. These are
1. Serialization ignores static fields, because they are not part of ay particular state state.
2. Base class fields are only hendled if the base class itself is serializable.
3. Transient fields.
42. Does Java provide any construct to find out the size of an object?
No, there is not sizeof operator in Java. So there is not direct way to determine the size of
an object directly in Java.

38. 43. What are wrapper classes?
Java provides specialized classes corresponding to each of the primitive data types. These
are called wrapper classes.
They are example: Integer, Character, Double etc.
44. Why do we need wrapper classes?
It is sometimes easier to deal with primitives as objects. Moreover most of the collection
classes store objects and not primitive data types. And also the wrapper classes provide
many utility methods also.
Because of these resons we need wrapper classes. And since we create instances of these
classes we can store them in any of the collection classes and pass them around as a
collection. Also we can pass them around as method parameters where a method expects
an object.
45. What are checked exceptions?
Checked exception are those which the Java compiler forces you to catch.
Example: IOException are checked exceptions.
46. What are runtime exceptions?
Runtime exceptions are those exceptions that are thrown at runtime because of either
wrong input data or because of wrong business logic etc. These are not checked by the
compiler at compile time.
47. What is the difference between error and an exception?
An error is an irrecoverable condition occurring at runtime. Such as OutOfMemory error.
These JVM errors and you can not repair them at runtime. While exceptions are
conditions that occur because of bad input etc. Example: FileNotFoundException will be
thrown if the specified file does not exist. Or a NullPointerException will take place if
you try using a null reference.
In most of the cases it is possible to recover from an exception (probably by giving user a
feedback for entering proper values etc.).
48. How to create custom exceptions?
Your class should extend class Exception, or some more specific type thereof.

39. 49. If I want an object of my class to be thrown as an exception object, what should I
do?
The class should extend from Exception class. Or you can extend your class from some
more precise exception type also.
50. If my class already extends from some other class what should I do if I want an
instance of my class to be thrown as an exception object?
One can not do anytihng in this scenarion. Because Java does not allow multiple
inheritance and does not provide any exception interface as well.
51. How does an exception permeate through the code?
An unhandled exception moves up the method stack in search of a matching When an
exception is thrown from a code which is wrapped in a try block followed by one or more
catch blocks, a search is made for matching catch block. If a matching type is found then
that block will be invoked. If a matching type is not found then the exception moves up
the method stack and reaches the caller method.
Same procedure is repeated if the caller method is included in a try catch block. This
process continues until a catch block handling the appropriate type of exception is found.
If it does not find such a block then finally the program terminates.
52. What are the different ways to handle exceptions?
There are two ways to handle exceptions,
1. By wrapping the desired code in a try block followed by a catch block to catch the
exceptions. and
2. List the desired exceptions in the throws clause of the method and let the caller of the
method hadle those exceptions.
53. Is it necessary that each try block must be followed by a catch block?
It is not necessary that each try block must be followed by a catch block. It should be
followed by either a catch block or a finally block. And whatever exceptions are likely to
be thrown should be declared in the throws clause of the method.
54. If I write return at the end of the try block, will the finally block still execute?
Yes even if you write return as the last statement in the try block and no exception
occurs, the finally block will execute. The finally block will execute and then the control
return.

40. 55. If I write System.exit(0); at the end of the try block, will the finally block still
execute?
No. In this case the finally block will not execute because when you say System.exit(0);
the control immediately goes out of the program, and thus finally never executes.
56. How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an
Observable object is updated it invokes the update() method of each of its observers to
notify the observers that it has changed state. The Observer interface is implemented by
objects that observe Observable objects.
57. What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of
multiple threads to shared resources.
Without synchronization, it is possible for one thread to modify a shared object while
another thread is in the process of using or updating that object's value. This often leads
to significant errors.
58. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by
the operation.
59. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is
possible for programs to use up memory resources faster than they are garbage collected.
It is also possible for programs to create objects that are not subject to garbage collection.
60. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting
or dead states or a higher priority task comes into existence.
Under time slicing, a task executes for a predefined slice of time and then reenters the
pool of ready tasks. The scheduler then determines which task should execute next, based
on priority and other factors.
61. When a thread is created and started, what is its initial state?
A thread is in the ready state after it has been created and started.

41. 62. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform
any cleanup processing before the object is garbage collected.
63. What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular
geographic, political, or cultural region.
64. What is the difference between a while statement and a do statement?
A while statement checks at the beginning of a loop to see whether the next loop iteration
should occur.
A do statement checks at the end of a loop to see whether the next iteration of a loop
should occur. The do statement will always execute the body of a loop at least once.
65. What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances
of a class. Non-static variables take on unique values with each object instance.
66. How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a
superclass constructor.
67. What is daemon thread and which method is used to create the daemon thread?
Daemon thread is a low priority thread which runs intermittently in the back ground
doing the garbage collection operation for the java runtime system.setDaemon method is
used to create a daemon thread.
68. Can applets communicate with each other?
At this point in time applets may communicate with other applets running in the same
virtual machine. If the applets are of the same class, they can communicate via shared
static variables. If the applets are of different classes, then each will need a reference to
the same class with static variables. In any case the basic idea is to pass the information
back and forth through a static variable.
An applet can also get references to all other applets on the same page using the
getApplets() method of java.applet.AppletContext. Once you get the reference to an
applet, you can communicate with it by using its public members.

42. It is conceivable to have applets in different virtual machines that talk to a server
somewhere on the Internet and store any data that needs to be serialized there. Then,
when another applet needs this data, it could connect to this same server. Implementing
this is non-trivial.
69. What are the steps in the JDBC connection?
While making a JDBC connection we go through the following steps :
Step 1 : Register the database driver by using :
Class.forName(" driver classs for that specific database" );
Step 2 : Now create a database connection using :
Connection con = DriverManager.getConnection(url,username,password);
Step 3: Now Create a query using :
Statement stmt = Connection.Statement("select * from TABLE NAME");
Step 4 : Exceute the query :
stmt.exceuteUpdate();
70. How does a try statement determine which catch clause should be used to handle
an exception?
When an exception is thrown within the body of a try statement, the catch clauses of the
try statement are examined in the order in which they appear. The first catch clause that is
capable of handling the exceptionis executed. The remaining catch clauses are ignored.
71. Can an unreachable object become reachable again?
An unreachable object may become reachable again. This can happen when the object's
finalize() method is invoked and the object performs an operation which causes it to
become accessible to reachable objects.
72. What method must be implemented by all threads?
All tasks must implement the run() method, whether they are a subclass of Thread or
implement the Runnable interface.
73. What are synchronized methods and synchronized statements?

43. Synchronized methods are methods that are used to control access to an object. A thread
only executes a synchronized method after it has acquired the lock for the method's object
or class.
Synchronized statements are similar to synchronized methods. A synchronized statement
can only be executed after a thread has acquired the lock for the object or class referenced
in the synchronized statement.
74. What is Externalizable?
Externalizable is an Interface that extends Serializable Interface. And sends data into
Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and
readExternal(ObjectInput in).
75. What modifiers are allowed for methods in an Interface?
Only public and abstract modifiers are allowed for methods in interfaces.
76. What are some alternatives to inheritance?
Delegation is an alternative to inheritance.
Delegation means that you include an instance of another class as an instance variable,
and forward messages to the instance. It is often safer than inheritance because it forces
you to think about each message you forward, because the instance is of a known class,
rather than a new class, and because it doesn't force you to accept all the methods of the
super class: you can provide only the methods that really make sense. On the other hand,
it makes you write more code, and it is harder to re-use (because it is not a subclass).
77. What does it mean that a method or field is "static"?
Static variables and methods are instantiated only once per class. In other words they are
class variables, not instance variables. If you change the value of a static variable in a
particular object, the value of that variable changes for all instances of that class.
Static methods can be referenced with the name of the class rather than the name of a
particular object of the class (though that works too). That's how library methods like
System.out.println() work out is a static field in the java.lang.System class.
78. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting
or dead states or a higher priority task comes into existence. Under time slicing, a task
executes for a predefined slice of time and then reenters the pool of ready tasks.

44. The scheduler then determines which task should execute next, based on priority and
other factors.
79. What is the catch or declare rule for method declarations?
If a checked exception may be thrown within the body of a method, the method must
either catch the exception or declare it in its throws clause.
80. Is Empty .java file a valid source file?
Yes. An empty .java file is a perfectly valid source file.
81. Can a .java file contain more than one java classes?
Yes. A .java file contain more than one java classes, provided at the most one of them is a
public class.
82. Is String a primitive data type in Java?
No. String is not a primitive data type in Java, even though it is one of the most
extensively used object. Strings in Java are instances of String class defined in java.lang
package.
83. Is main a keyword in Java?
No. main is not a keyword in Java.
84. Is next a keyword in Java?
No. next is not a keyword.
85. Is delete a keyword in Java?
No. delete is not a keyword in Java. Java does not make use of explicit destructors the
way C++ does.
86. Is exit a keyword in Java?
No. To exit a program explicitly you use exit method in System object.
87. What happens if you dont initialize an instance variable of any of the primitive
types in Java?
Java by default initializes it to the default value for that primitive type. Thus an int will be
initialized to 0(zero), a boolean will be initialized to false.

45. 88. What will be the initial value of an object reference which is defined as an
instance variable?
The object references are all initialized to null in Java. However in order to do anything
useful with these references, you must set them to a valid object, else you will get
NullPointerExceptions everywhere you try to use such default initialized references.
89. What are the different scopes for Java variables?
The scope of a Java variable is determined by the context in which the variable is
declared. Thus a java variable can have one of the three scopes at any given point in time.
1. Instance : - These are typical object level variables, they are initialized to default
values at the time of creation of object, and remain accessible as long as the object
accessible.
2. Local : - These are the variables that are defined within a method. They remain
accessbile only during the course of method excecution. When the method finishes
execution, these variables fall out of scope.
3. Static: - These are the class level variables. They are initialized when the class is
loaded in JVM for the first time and remain there as long as the class remains loaded.
They are not tied to any particular object instance.
90. What is the default value of the local variables?
The local variables are not initialized to any default value, neither primitives nor object
references. If you try to use these variables without initializing them explicitly, the java
compiler will not compile the code. It will complain abt the local varaible not being
initilized.
91. How many objects are created in the following piece of code?
MyClass c1, c2, c3;
c1 = new MyClass ();
c3 = new MyClass ();
Only 2 objects are created, c1 and c3. The reference c2 is only declared and not
initialized.
92. Can a public class MyClass be defined in a source file named YourClass.java?
No. The source file name, if it contains a public class, must be the same as the public
class name itself with a .java extension.
93. Can main() method be declared final?

46. Yes, the main() method can be declared final, in addition to being public static.
94. What is HashMap and Map?
Map is an Interface and Hashmap is the class that implements Map.
95. Difference between HashMap and HashTable?
The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized
and permits nulls. (HashMap allows null values as key and value whereas Hashtable
doesnt allow).
HashMap does not guarantee that the order of the map will remain constant over time.
HashMap is unsynchronized and Hashtable is synchronized.
96. Difference between Vector and ArrayList?
Vector is synchronized whereas arraylist is not.
97. Difference between Swing and Awt?
AWT are heavy-weight componenets. Swings are light-weight components. Hence swing
works faster than AWT.
98. What will be the default values of all the elements of an array defined as an
instance variable?
If the array is an array of primitive types, then all the elements of the array will be
initialized to the default value corresponding to that primitive type.
Example: All the elements of an array of int will be initialized to 0(zero), while that of
boolean type will be initialized to false. Whereas if the array is an array of references (of
any type), all the elements will be initialized to null.
ADVANCED JAVA
. What is a transient variable?
A transient variable is a variable that may not be serialized.
2. Which containers use a border Layout as their default layout?
The Window, Frame and Dialog classes use a border layout as their default layout.
3. Why do threads block on I/O?

47. Threads block on I/O (that is enters the waiting state) so that other threads may execute
while the I/O Operation is performed.
4. How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an
Observable object is updated it invokes the update() method of each of its observers to
notify the observers that it has changed state. The Observer interface is implemented by
objects that observe Observable objects.
5. What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of
multiple threads to shared resources. Without synchronization, it is possible for one
thread to modify a shared object while another thread is in the process of using or
updating that object's value. This often leads to significant errors.
6. Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object..
7. What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
8. Is null a keyword?
The null is not a keyword.
9. What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the
component to display normally.
10. What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.
11. Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.
12. What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.

48. 13. What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on
collections of objects.
14. Which characters may be used as the second character of an identifier, but not
as the first character of an identifier?
The digits 0 through 9 may not be used as the first character of an identifier but they may
be used after the first character of an identifier.
15. What is the List interface?
The List interface provides support for ordered collections of objects.
16. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by
the operation.
17. What is the Vector class?
The Vector class provides the capability to implement a growable array of objects
18. What modifiers may be used with an inner class that is a member of an outer
class?
A (non-local) inner class may be declared as public, protected, private, static, final, or
abstract
19. What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.
20. What is the difference between the >> and >>> operators?
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have
been shifted out.
21. Which method of the Component class is used to set the position and size of a
component?
setBounds() method is used to set the position and size of a component.
22. What is the difference between yielding and sleeping?

49. When a task invokes its yield() method, it returns to the ready state. When a task invokes
its sleep() method, it returns to the waiting state.
23. Which java.util classes and interfaces support event handling?
The EventObject class and the EventListener interface support event processing.
24. Is sizeof a keyword?
The sizeof operator is not a keyword
25. What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.
26. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is
possible for programs to use up memory resources faster than they are garbage collected.
It is also possible for programs to create objects that are not subject to garbage collection.
27. What restrictions are placed on the location of a package statement within a
source code file?
A package statement must appear as the first line in a source code file (excluding blank
lines and comments).
28. Can an object's finalize() method be invoked while it is reachable?
An object's finalize() method cannot be invoked by the garbage collector while the object
is still reachable. However, an object's finalize() method may be invoked by other
objects.
29. What is the immediate superclass of the Applet class?
Panel.
30. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting
or dead states or a higher priority task comes into existence. Under time slicing, a task
executes for a predefined slice of time and then reenters the pool of ready tasks.
The scheduler then determines which task should execute next, based on priority and
other factors.

50. 31. Name three Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.
32. What value does readLine() return when it has reached the end of a file?
The readLine() method returns null when it has reached the end of a file.
33. What is the immediate superclass of the Dialog class?
Window.
34. What is clipping?
Clipping is the process of confining paint operations to a limited area or shape.
35. What is a native method?
A native method is a method that is implemented in a language other than Java.
36. Can a for statement loop indefinitely?
Yes, a for statement can loop indefinitely. For example, consider the following:
for(;;) ;
37. What are order of precedence and associativity, and how are they used?
Order of precedence determines the order in which operators are evaluated in
expressions.
Associatity determines whether an expression is evaluated left-to-right or right-to-left.
38. When a thread blocks on I/O, what state does it enter?
A thread enters the waiting state when it blocks on I/O.
39. To what value is a variable of the String type automatically initialized?
The default value of an String type is null.
40. What is the catch or declare rule for method declarations?
If a checked exception may be thrown within the body of a method, the method must
either catch the exception or declare it in its throws clause.

51. 41. What is the difference between a MenuItem and a CheckboxMenuItem?
The CheckboxMenuItem class extends the MenuItem class to support a menu item that
may be checked or unchecked.
42. What is a task's priority and how is it used in scheduling?
A task's priority is an integer value that identifies the relative order in which it should be
executed with respect to other tasks. The scheduler attempts to schedule higher priority
tasks before lower priority tasks.
43. What class is the top of the AWT event hierarchy?
The java.awt.AWTEvent class is the highest-level class in the AWT event-class
hierarchy.
44. When a thread is created and started, what is its initial state?
A thread is in the ready state after it has been created and started.
45. Can an anonymous class be declared as implementing an interface and
extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be
declared to do both.
46. What is the immediate superclass of Menu?
MenuItem.
47. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform
any cleanup processing before the object is garbage collected.
48. Which class is the immediate superclass of the MenuComponent class?
Object.
49. What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM
invokes the thread's run() method when the thread is initially executed.
50. What is the difference between the Boolean & operator and the && operator?

52. If an expression involving the Boolean & operator is evaluated, both operands are
evaluated. Then the & operator is applied to the operand. When an expression involving
the && operator is evaluated, the first operand is evaluated.
If the first operand returns a value of true then the second operand is evaluated. The &&
operator is then applied to the first and second operands. If the first operand evaluates to
false, the evaluation of the second operand is skipped.
51. Name three subclasses of the Component class.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or
TextComponent.
52. What is the GregorianCalendar class?
The GregorianCalendar class provides support for traditional Western calendars.
53. Which Container method is used to cause a container to be laid out and
redisplayed?
validate() method is used to cause a container to be laid out and redisplayed.
54. What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.
55. How many times may an object's finalize() method be invoked by the garbage
collector?
An object's finalize() method may only be invoked once by the garbage collector.
56. What is the purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to provide the capability to execute code no matter whether or
not an exception is thrown or caught.
57. What is the argument type of a program's main() method?
A program's main() method takes an argument of the String[] type.
58. Which Java operator is right associative?
The = operator is right associative.
59. Can a double value be cast to a byte?

53. Yes, a double value can be cast to a byte.
60. What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its
implements clause.
61. What method is invoked to cause an object to begin executing as a separate
thread?
The start() method of the Thread class is invoked to cause an object to begin executing as
a separate thread.
62. Name two subclasses of the TextComponent class.
TextField and TextArea.
63. Which containers may have a MenuBar?
Frame.
64. How are commas used in the intialization and iteration parts of a for statement?
Commas are used to separate multiple statements within the initialization and iteration
parts of a for statement.
65. What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(), notify(), and notifyAll() methods are used to provide an efficient way for
threads to wait for a shared resource. When a thread executes an object's wait() method, it
enters the waiting state. It only enters the ready state after another thread invokes the
object's notify() or notifyAll() methods..
66. What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.
67. How are Java source code files named?
A Java source code file takes the name of a public class or interface that is defined within
the file. A source code file may contain at most one public class or interface. If a public
class or interface is defined within a source code file, then the source code file must take
the name of the public class or interface.

54. If no public class or interface is defined within a source code file, then the file must take
on a name that is different than its classes and interfaces. Source code files use the .java
extension.
68. What is the relationship between the Canvas class and the Graphics class?
A Canvas object provides access to a Graphics object via its paint() method.
69. What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.
70. What value does read() return when it has reached the end of a file?
The read() method returns -1 when it has reached the end of a file.
71. Can a Byte object be cast to a double value?
No. An object cannot be cast to a primitive value.
72. What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of
the class's outer class.
A static inner class does not have any object instances.
73. What is the difference between the String and StringBuffer classes?
String objects are constants. StringBuffer objects are not constants.
74. If a variable is declared as private, where may the variable be accessed?
A private variable may only be accessed within the class in which it is declared.
75. What is an object's lock and which object's have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized
access to the object. A thread may execute a synchronized method of an object only after
it has acquired the object's lock.
All objects and classes have locks. A class's lock is acquired on the class's Class object.
76. What is the Dictionary class?

55. The Dictionary class provides the capability to store key-value pairs.
77. How are the elements of a BorderLayout organized?
The elements of a BorderLayout are organized at the borders (North, South, East, and
West) and the center of a container.
78. What is the % operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing
the first operand by the second operand.
79. When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the
referenced interface.
80. What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a
menu bar.
81. Which class is extended by all other classes?
The Object class is extended by all other classes.
82. Can an object be garbage collected while it is still reachable?
A reachable object cannot be garbage collected. Only unreachable objects may be
garbage collected..
83. Is the ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.
84. What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific properties, such as
ascent and descent, of a Font object.
85. How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.
86. What happens when a thread cannot acquire a lock on an object?

56. If a thread attempts to execute a synchronized method or synchronized statement and is
unable to acquire an object's lock, it enters the waiting state until the lock becomes
available.
87. What is the difference between the Reader/Writer class hierarchy and the
InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the
InputStream/OutputStream class hierarchy is byte-oriented.
88. What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This
includes the Error and Exception types.
89. If a class is declared without any access modifiers, where may the class be
accessed?
A class that is declared without any access modifiers is said to have package access. This
means that the class can only be accessed by other classes and interfaces that are defined
within the same package.
90. What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.
91. What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with
values.
92. Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.
93. For which statements does it make sense to use a label?
The only statements for which it makes sense to use a label are those statements that can
enclose a break or continue statement.
94. What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.
95. Which TextComponent method is used to set a TextComponent to the read-only
state?