Dr. Avadhesh Kumar
Asst. Prof, SAS, VIT-AP
Object Oriented Programming

 Object-oriented programming (OOP) is a
computer programming model that organizes
software design around data, or objects,
rather than functions and logic. An object can
be defined as a data field that has unique
attributes and behavior.
 Every class has data field(data member) and
method(function).

 A Java object is an instance of a Java class.
Each object has an identity, a behavior and a
state.
 The state of an object is stored in fields
(variables), while methods (functions) display
the object's behavior. Objects are created at
runtime from templates, which are also
known as classes.

 A class is a template or blueprint from which
objects are created. So, an object is the
instance(result) of a class.

 Originally, object-oriented programming was
used most frequently for two major types of
applications:
 Computer simulations,
which attempt to mimic real-world activities
so that their processes can be improved or so
that users can better understand how the
real-world processes operate
 Graphical user interfaces, or GUIs
(pronounced “gooeys”), which allow users to
interact with a program in a graphical
environment

 To understand object-oriented programming
it requires grasping three basic concepts:
 1. Encapsulation
 2. Inheritance
 3. Polymorphism

 A method is a self-contained block of
program code that carries out some action,
similar to a procedure (function) in a
procedural program (C program).
 It is like a function in C program but it is
associated some class.
 For example, a Dog class might have
methods for walking, eating.

 In object-oriented classes, attributes and
methods are encapsulated into objects.
 Encapsulation is the enclosure of data and
methods within an object.
 Encapsulation allows you to treat all of an
object’s methods and data as a single entity.
Just as an actual dog contains all of its
attributes and abilities, so would a program’s
Dog object.

 Encapsulation also refers to the concealment
of an object’s data and methods from outside
sources.
 Concealing data is sometimes called
information hiding.
 Encapsulation lets you hide specific object
attributes and methods from outside sources
and provides the security that keeps data and
methods safe from inadvertent(undesired)
changes.

 An important feature of object-oriented program
design is inheritance—the ability to create
classes that share the attributes and methods of
existing classes, but with more specific features.
 For example, Automobile is a class, and all
Automobile objects share many traits and
abilities. Convertible is a class that inherits from
the Automobile class; a Convertible is a
type of Automobile that has and can do
everything a “plain” Automobile does—but with
an added ability

 A final important concept in object-oriented
terminology is polymorphism.
 Literally, polymorphism means “many
forms”—it describes the feature of languages
that allows the same word or symbol to be
interpreted correctly in different situations
based on the context.
 For example, although the classes
Automobile, Sailboat, and Airplane all inherit
from Vehicle, turn and stop methods work
differently for instances of those classes.

 It is a Java standard, although not a requirement, to begin
class identifiers with an uppercaseletter and employ other
uppercase letters as needed to improve readability.
 (By contrast, method identifiers, like println(), conventionally
begin with a lowercase letter.)
 The stylethat joins words in which each word begins with an
uppercase letter is called Pascal casing, or sometimes upper
camel casing. You should follow established conventions for
Java so
 your programs will be easy for other programmers to
interpret and follow.

 To create a Scanner object and connect it to the
System.in object, you write a statement similar to
the following:
 Scanner inputDevice = new Scanner(System.in);

 A main() method executes automatically when
you run a program, but other methods do not
execute simply because you place them
within a class—they must be called.
 The method header is the first line of a
method. It contains the following:
 Optional access specifiers
 A return type
 An identifier
 Parentheses

 It is a special type of method which is used to
initialize the object.
 Every time an object is created using the
new() keyword, at least one constructor is
called.
 It calls a default constructor if there is no
constructor available in the class. In such
case, Java compiler provides a default
constructor by default.

 Constructor name must be the same as its
class name
 There are two types of constructors in Java:
 1. Default constructor (no-arg constructor)
 2. Parameterized constructor

 The access modifiers in Java specifies the
accessibility or scope of a field, method,
constructor, or class.
 We can change the access level of fields,
constructors, methods, and class by applying
the access modifier on it.

 Private: The access level of a private modifier is only
within the class. It cannot be accessed from outside
the class.
 Default: The access level of a default modifier is only
within the package. It cannot be accessed from
outside the package. If you do not specify any access
level, it will be the default.
 Protected: The access level of a protected modifier is
within the package and outside the package through
child class. If you do not make the child class, it
cannot be accessed from outside the package.
 Public: The access level of a public modifier is
everywhere. It can be accessed from within the class,
outside the class, within the package and outside the
package