Java InterView Questions

  Interview Faqs by   Srinivas Mahanti

Oracle InterViewQusetions 11-15

11. what is null value?
Null Value is neither zero nor it is a blank space. It is some unknown value which occupies 4 bytes of space of memory in SQL.

12. Define transaction?
A transaction is a sequence of SQL statements that Oracle Database treats as a single unit.

13. what is the difference between sql&oracle?
SQL is Stuctured Query Language.Oracle is a Database.SQL is used to write queries against Oracle DB.

14. What are different Oracle database objects?
TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES

15. What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

Oracle InterView Questions 6-10

6. What is the difference between clustered and a non-clustered index?
A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A Non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk.

7. What is a Table-space?
A database is divided into Logical Storage Unit called tablespace. A tablespace is used to grouped related logical structures together.

8. Why use materialized view instead of a table?
Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution.

9. What does ROLLBACK do?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.

10. Compare and contrast TRUNCATE and DELETE for a table?
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.

Oracle InterView Questions

1.what is Oracle Table?
A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

2. What are Clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

3. What is an Index?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

4. What are the advantages of views?

• Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.
• Hide data complexity.
• Simplify commands for the user.
• Present the data in a different perspective from that of the base table
• Store complex queries.

5. What are the various types of queries?
The types of queries are :

• Normal Queries
• Sub Queries
• Co-related queries
• Nested queries
• Compound queries

What is a container class? What are the types of container classes?

A container class is a class that is used to hold objects in memory or external storage. A container class acts as a generic holder. A container class has a predefined behavior and a well-known interface. A container class is a supporting class whose purpose is to hide the topology used for maintaining the list of objects in memory. When a container class contains a group of mixed objects, the container is called a heterogeneous container; when the container is holding a group of objects that are all the same, the container is called a homogeneous container.

How can I handle a destructor that fails?

Write a message to a log-file. But do not throw an exception.
The C++ rule is that you must never throw an exception from a destructor that is being called during the "stack unwinding" process of another exception. For example, if someone says throw Foo(), the stack will be unwound so all the stack frames between the throw Foo() and the } catch (Foo e) { will get popped. This is called stack unwinding.
During stack unwinding, all the local objects in all those stack frames are destructed. If one of those destructors throws an exception (say it throws a Bar object), the C++ runtime system is in a no-win situation: should it ignore the Bar and end up in the } catch (Foo e) { where it was originally headed? Should it ignore the Foo and look for a } catch (Bar e) { handler? There is no good answer -- either choice loses information.
So the C++ language guarantees that it will call terminate() at this point, and terminate() kills the process. Bang you're dead.

What is an Iterator class?

A class that is used to traverse through the objects maintained by a container class. There are five categories of iterators: input iterators, output iterators, forward iterators, bidirectional iterators, random access. An iterator is an entity that gives access to the contents of a container object without violating encapsulation constraints. Access to the contents is granted on a one-at-a-time basis in order. The order can be storage order (as in lists and queues) or some arbitrary order (as in array indices) or according to some ordering relation (as in an ordered binary tree). The iterator is a construct, which provides an interface that, when called, yields either the next element in the container, or some value denoting the fact that there are no more elements to examine. Iterators hide the details of access to and update of the elements of a container class. Something like a pointer.

What problem does the namespace feature solve?

Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries. The namespace feature surrounds a library's external declarations with a unique namespace that eliminates the potential for those collisions.
namespace [identifier] { namespace-body }
A namespace declaration identifies and assigns a name to a declarative region.
The identifier in a namespace declaration must be unique in the declarative region in which it is used. The identifier is the name of the namespace and is used to reference its members.

What is virtual function?

When derived class overrides the base class method by redefining the same function, then if client wants to access redefined the method from derived class through a pointer from base class object, then you must define this function in base class as virtual function.
class parent
{
   void Show()
{
cout << "i'm parent" << endl;
}
};

class child: public parent
{
   void Show()
{
cout << "i'm child" << endl;
}
};

parent * parent_object_ptr = new child;
parent_object_ptr->show() // calls parent->show() i

now we goto virtual world...
class parent
{
   virtual void Show()
{
cout << "i'm parent" << endl;
}
};

class child: public parent
{
   void Show()
{
cout << "i'm child" << endl;
}
};

parent * parent_object_ptr = new child;
parent_object_ptr->show() // calls child->show() 

When are temporary variables created by C++ compiler?

Provided that function parameter is a "const reference", compiler generates temporary variable in following 2 ways.
a) The actual argument is the correct type, but it isn't Lvalue
double Cube(const double & num)
{
num = num * num * num;
return num;
}
double temp = 2.0;
double value = cube(3.0 + temp); // argument is a expression and not a Lvalue;

b) The actual argument is of the wrong type, but of a type that can be converted to the correct type
long temp = 3L;
double value = cuberoot ( temp); // long to double conversion

What is passing by reference?

Method of passing arguments to a function which takes parameter of type reference.
for example:
void swap( int & x, int & y )
{
int temp = x;
x = y;
y = temp;
}
int a=2, b=3;
swap( a, b );

Basically, inside the function there won't be any copy of the arguments "x" and "y" instead they refer to original variables a and b. so no extra memory needed to pass arguments and it is more efficient.

What are storage qualifiers in C++ ?

They are..
const
volatile
mutable
Const keyword indicates that memory once initialized, should not be altered by a program.
volatile keyword indicates that the value in the memory location can be altered even though nothing in the program
code modifies the contents. for example if you have a pointer to hardware location that contains the time, where hardware changes the value of this pointer variable and not the program. The intent of this keyword to improve the optimization ability of the compiler.
mutable keyword indicates that particular member of a structure or class can be altered even if a particular structure variable, class, or class member function is constant.
struct data
{
char name[80];
mutable double salary;
}
const data MyStruct = { "Satish Shetty", 1000 }; //initlized by complier
strcpy ( MyStruct.name, "Shilpa Shetty"); // compiler error
MyStruct.salaray = 2000 ; // complier is happy allowed

What is difference between template and macro??

There is no way for the compiler to verify that the macro parameters are of compatible types. The macro is expanded without any special type checking.
If macro parameter has a postincremented variable ( like c++ ), the increment is performed two times.
Because macros are expanded by the preprocessor, compiler error messages will refer to the expanded macro, rather than the macro definition itself. Also, the macro will show up in expanded form during debugging.
for example:
Macro:
#define min(i, j) (i < j ? i : j)
template:
template
T min (T i, T j)
{
return i < j ? i : j;
}

Constructor & Destructors in C

What is constructor or ctor?
Constructor creates an object and initializes it. It also creates vtable for virtual functions. It is different from other methods in a class.

What is destructor?
Destructor usually deletes any extra resources allocated by the object.

What is default constructor?
Constructor with no arguments or all the arguments has default values.

What is copy constructor?
Constructor which initializes the it's object member variables ( by shallow copying) with another object of the same class. If you don't implement one in your class then compiler implements one for you.
for example:
Boo Obj1(10); // calling Boo constructor
Boo Obj2(Obj1); // calling boo copy constructor
Boo Obj2 = Obj1;// calling boo copy constructor
When are copy constructors called?
Copy constructors are called in following cases:
a) when a function returns an object of that class by value
b) when the object of that class is passed by value as an argument to a function
c) when you construct an object based on another object of the same class
d) When compiler generates a temporary object

What will happen if any string in c is converted to integer explicitly?

 If we try to convert string into integer explicitly then string’s address will get stored in integer. 
int main()
{ 
 char *a="abhas";
 int b=(int)a;
 // now b will hold address of a 
}

Memory Leak, Union, Heap,Stack in C

What is a memory leak?

Memory leak is that when memory is allocated but its not released because of an application consume memory reducing the available memory for other applications and causing the system to page virtual memory to the hard drive showing the application or crashing the application. When the computer memory resource limits are reached.

 Explain about storage of union elements.

The key point about storage of union elements is that Union elements are use to share common memory space.

What is the difference between the Heap and the Stack?

The main difference b/n the Heap and the Stack are given below:

- In stack we create object temporary where programmer used to reserve allocation.'
- stack not have automatic garbage collection where as heap have automatic garbage collection.

How the processor registers can be used in C?

using keyword register we can use the process register in C.Basically process register is used to store variables those i want to access frequently.if these registers are not used in any other program,then those registers we used to allocate memory these variables.

What are the stream files?

We can open file in C with using stream files.which are identified with a pointer to a FILE structure, or as low-level files, which are identified with an integer handle. We can open stream files with using one of the following functions.

fopen(): Opens the specified file with the specified mode 

freopen(): Closes the file specified, then opens a new file as specified 

fdopen(): Opens a duplicate stream file for an already open low-level file

What are the major differences between C and C++?

C was the C++ predecessor. As it's name implies, a lot of C remains in C++. Although not actually being more powerful than C, C++ allows the programmer to more easily manage and operate with Objects, using an OOP (Object Oriented Programming) concept.

C++ allows the programmer to create classes, which are somewhat similar to C structures. However, to a class can be assigned methods, functions associated to it, of various prototypes, which can access and operate within the class, somewhat like C functions often operate on a supplied handler pointer.

Although it is possible to implement anything which C++ could implement in C, C++ aids to standarize a way in which objects are created and managed, whereas the C programmer who implements the same system has a lot of liberty on how to actually implement the internals, and style among programmers will vary a lot on the design choices made.

In C, some will prefer the handler-type, where a main function initializes a handler, and that handler can be supplied to other functions of the library as an object to operate on/through. Others will even want to have that handler link all the related function pointers within it which then must be called using a convention closer to C++.

To finish this discussion, C++ applications are generally slower at runtime, and are much slower to compile than C programs. The low-level infrastructure for C++ binary execution is also larger. For these reasons C is always commonly used even if C++ has alot of popularity, and will probably continue to be used in projects where size and speed are primary concerns, and portable code still required (assembly would be unsuitable then).

What is a container class? What are the different types of container classes?

A container class is a class that is used to hold objects in memory or external storage. A container class acts as a generic holder. A container class has a predefined behavior and a well-known interface. A container class is a supporting class whose purpose is to hide the

topology used for maintaining the list of objects in memory. When a container class contains a group of mixed objects, the container is called a heterogeneous container; when the container is holding a group of objects that are all the same, the container is called a homogeneous

container.