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# Nagaraju

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### Nagaraju

1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.
41. 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. 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?