Q)
What is object oriented programming language?
Object-orientation
is
a set of tools and methods that enable software engineers to build reliable, user friendly,
maintainable, well documented, reusable software. System that fulfills the requirements of
its users. It is claimed that object-orientation provides software developers
with new mind tools to use in solving a wide variety of problems.
Object-orientation provides a new view of computation. a software system is
seen as a community of objects
that cooperate with each other by
passing messages in solving a problem.
An
object-oriented programming language provides support for the following
object-oriented concepts:
·
objects
and classes
·
inheritance
·
polymorphism
and dynamic binding
Q)
What are the Principles of object oriented programming?
Object orientation is of the programming
styles or methodologies. As far as application development is concerned,
following are the important object oriented features.
1. Encapsulation
2. Inheritance
3. Polymorphism
Encapsulation:
The concept of binding the data along with its related
and corresponding functionalities or functions is known as encapsulation.
The concept of making the
data available only to certain
related areas or only within mentioned borders is known as binding.
Inheritance:
A key feature of JAVA classes is inheritance.
Inheritance allows to create classes which are derived from other classes, so
that they automatically include some of its "parent's" members, plus
its own.
The concept of getting the
properties of one class to another
class is known as inheritance.
Polymorphism:
Poly means many and
morphism means forms (functionalities), so the concept of defining multiple
functionalities or methods with the same name associated with the same object
is known as polymorphism.
Q)
Give any four advantages of OOPS.
1.
The
principle of data hiding helps the programmer to build secure programs
That cannot be invaded
by code in other parts of the program.
2.
It is
possible to have multiple instances of an object to co-exist without any
Interference
3.
Object
oriented programming can be easily upgraded from small to large systems.
4.
Software
complexity can be easily managed.
Q) Give any four applications of OOPS
Ø Real-time systems.
Ø Simulation and modeling.
Ø Object-oriented databases.
Ø AI and expert systems.
Q)
What Is Class?
- Class
is nothing but a structure binding the data along with its corresponding
and related functions.
- Class
is a user defined data type in java. Class will act as the base for
encapsulation.
- Class
is a similar (but not exactly) to “structure” in c programming language to
create user defined data types that model real world entities.
- Class
is a not an object oriented feature. But class is the means with which all
object oriented features are programmatically realized. For example,
encapsulation, polymorphism and inheritance can’t be programmatically
achieved without class concept. But it does not mean that class is an
object oriented feature.
- A
class contain properties and operations
- A
class is a plan for the proposed object.
- A
class is known as a blueprint or template for an object.
- Defining
a class is nothing but modeling a real world entity. Real world entity
type creation is nothing but classification. That is why the name “class”
which is nothing but type.
- Any
java application works like collection of classes.
Q)
What is general form class definition?
General form of a class definition:
class
classname {
type instance-variable1;
type instance-variable2;
//
...
type instance-variableN;
type methodname1(parameter-list) {
//
body of method
}
type methodname2(parameter-list) {
//
body of method
}
//
...
type methodnameN(parameter-list) {
//
body of method
}
}
Q) What is object?
·
Physical realization of a class is nothing
but an object.
·
Instantiating a class is nothing but
creating an object.
·
A class is the basic of encapsulation. An
object implements encapsulation.
·
From class any number of objects of can be
created.
·
Object is nothing but some memory area in
RAM to store data in a secured manner.
·
Fundamental unit of data storage in an
object oriented system to store data in secured manner is nothing but an
object.
An
object is associated with 3 things:
1.
State
2.
Behavior
3.
Identity
·
Properties/variable/attributes and data
stored at that time in those variables put together is nothing but state of the
object. I.e. data stored in an object is known as object state.
·
Operations/methods of the object are
nothing but object behavior.
·
Name of the object with which it is
uniquely identified is nothing but identify of an object.
Q) What is the need of object?
Ans:
In order to allocate memory space and load the members of a class to the RAM
from the byte code at the Run time we need object.
Q) Explain Creating Objects in Java?
->
We know that a class is a collection of variables and the methods that access
those variables. Generally, when a program starts execution, the JVM first
loads the main() method into memory and starts execution. Because the main() is
residing in memory, the remaining members of the class are not available to
main(). To make the remaining members of a class(non-static) available to
main(), we create objects. That is ,an Object is the memory created for the
members (non-static) of a class. The procedure for creating an object is as
follows:
• Obtaining
objects of a class is a two-step process.
• First,
declare a variable of the class type. This variable does not define an object.
Instead, it is simply a variable that can refer to an object.
class-name
reference;
• Second,
acquire an actual, physical copy of the object and assign it to that variable
using the new operator.
reference
= new class-name();
• The
new operator dynamically allocates (that is, allocates at run time) memory for
an object and returns a reference to it.
• This
reference is, more or less, the address in memory of the object allocated by
new.
• This
reference is then stored in the variable. Thus, in Java, all class objects must
be dynamically allocated.
•
At this point, you
might be wondering why you do not need to use new for such things as integers or characters.
•
The answer is that
Java’s simple types are not implemented as objects.
•
Rather, they are
implemented as “normal” variables. This is done in the interest of efficiency.
•
It is important to
understand that new allocates
memory for an object during run time.
•
The advantage of this approach is that your program
can create as many or as few objects as it needs during the execution of your
program.
For
example, for a class Sample, we can create an object as follows :
Sample
s;
s
= new Sample();
->We
can also create an object in a single statement as follows:
class-name reference =
new class-name();
Eg : Sample
s = new Sample();
->
Once
the object is created, we can access the class members in main() using the
dot(.) operator.
Q)
What object contains?
Ans:
Object of any class contains only data. Object of a class would not contain the
logics or the functionalities of a function.
Q)
If you modify one object data will another object data also be modified?
No,
modifications
done for one object will not be affected to another object.
Q)
Till what period of time object of a class would be persistent?
Ans:
As long as address of the object is persistent, the object is also persistent
in the ram. Once address of the object is loss, Automatically the corresponding
object deleted from the ram.
Q)
When object is available to a method?
Ans:
whenever
we make a method call with an object and if the functionality of a method is
loaded to the ram because of an object, then we can says that object is
available for that method.
All the non-static members
of a class would be directly available to every non–static method of the same
class.
Q)
What are the instance variable?
Ans:
Any non static variable of a class can be called as an instance variable. All
the non static variables of a class would be loaded to the ram through an
instance of class. And there all present inside of a class thus these variables
are known as instance variable.
Q)
What is the difference between a reference variable and pointer variable in
java?
Ans: A
pointer variable contains the actual address but where as a reference variable
contains only the index of the address.
The actual address of an
object would be maintained by the jvm internally and that can be seen by the
end user. Thus people say that java doesn’t support pointers. But java support
pointers, that pointer are called as restricted pointers. Restricted pointers
mean pointers without arithmetic support.
Q)
What is dynamic Binding?
Linking the statements of
a method when it is called, is called “Binding”. If the statements of a method
are linked at the time of program compilation, it is called “Static Binding”
(E.g.: C-Language). If the statements of a method are linked at the time of
program execution, it is called “Dynamic Binding” (E.g.: OO languages).
Q)
What is message passing?
Objects communicate with
each other by passing messages between them which we call message passing.
Message Passing involves:
- creating
classes
- creating
object
- establishing
link with objects
E.g.:
b. deposit (SB2045,20000);
Q)
What is Data Abstraction?
The major goal of OOP is
“Data Security”. This can be achieved by hiding variables of a class from
external functions. This concept of hiding the data members of a class from
outside functions is called “Data Abstraction”.
Q) What are different types of inner classes?
A) Nested top-level classes-
If you declare a class within a class and specify the static modifier, the
compiler treats the class just like any other top-level class. Any class
outside the declaring class accesses the nested class with the declaring class
name acting similarly to a package. e.g., outer. Inner. Top-level inner classes
implicitly have access only to static variables. There can also be inner
interfaces. All of these are of the nested top-level variety.
Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a more publicly available interface. Because local classes are not members the modifiers public, protected, private and static are not usable.
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.
Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a more publicly available interface. Because local classes are not members the modifiers public, protected, private and static are not usable.
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.
Inner
class inside method cannot have static members or blocks
Q)
How to declare classes, methods and attributes in java?
Declaring Classes:
<Access_Specifier> class <Class_name> {
<attribute
declaration>;
<constructor
declaration>;
<Method
declaration>
}
Declaring Attributes:
<Access_Specifier>
<type> <name>=<initial-value>;
Declaring Methods:
<Access_Specifier>
<return_type> <name>( <argument>){
<statements>
}
Q) What is the
difference between procedural and object-oriented programs?
1. In procedural program, programming logic follows certain procedures and the instructions are executed one after another. In OOP program, unit of program is object, which is nothing but combination of data and code.
2. In procedural program, data is exposed to the whole program whereas in OOPs program, it is accessible within the object and which in turn assures the security of the code.
1. In procedural program, programming logic follows certain procedures and the instructions are executed one after another. In OOP program, unit of program is object, which is nothing but combination of data and code.
2. In procedural program, data is exposed to the whole program whereas in OOPs program, it is accessible within the object and which in turn assures the security of the code.
Q) Differentiate
between the message and method.
Message
* Objects communicate by sending messages to each other.
* A message is sent to invoke a method.
Method
* Provides response to a message
* It is an implementation of an operation.
Message
* Objects communicate by sending messages to each other.
* A message is sent to invoke a method.
Method
* Provides response to a message
* It is an implementation of an operation.
Q) 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. UTF-16 uses 16-bit and larger bit patterns..
Q) Is size of a keyword?
The size of
operator is not a keyword..
Q) 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.
