Object oriented programming CLASSES-AND-OBJECTS.pptx

Classes and Objects
• In Java, classes and objects are basic concepts of
Object Oriented Programming (OOPs) that are used to
represent real-world concepts and entities. The class
represents a group of objects having similar properties
and behavior.

For example, the animal type Dog is a class while a
particular dog named Tommy is an object of
the Dog class.

Classes
A class in Java is a set of objects which shares common
characteristics/ behavior and common properties/
attributes. It is a user-defined blueprint or prototype
from which objects are created. For example, Student is a
class while a particular student named Ravi is an object.

Properties of Java Classes
1.Class is not a real-world entity. It is just a template or blueprint
or prototype from which objects are created.
2.Class does not occupy memory.
3.Class is a group of variables of different data types and a group
of methods.
• Data member
• Method
• Constructor
• Nested Class
• Interface

Components of Java Classes
1.Modifiers: A class can be public or has default access
2.Class keyword: class keyword is used to create a class.
3.Class name: The name should begin with an initial letter
(capitalized by convention).
4.Superclass(if any): The name of the class’s parent
(superclass), if any, preceded by the keyword extends. A class
can only extend (subclass) one parent.
5.Interfaces(if any): A comma-separated list of interfaces
implemented by the class, if any, preceded by the keyword
implements. A class can implement more than one interface.
6.Body: The class body is surrounded by braces, { }.

Access modifiers for classes or
interfaces
But, the classes and interfaces themselves can have only
two access modifiers when declared outside any other
class.
1) public
2) default (when no access modifier is specified)
Note: Nested interfaces and classes can have all access
modifiers.
Note: We cannot declare class/interface with private or
protected access modifiers.

Access modifiers for classes or
interfaces
In Java, methods and data members can be encapsulated by
the following four access modifiers. The access modifiers are
listed according to their restrictiveness order.
1) private (accessible within the class where defined)
2) default or package-private (when no access modifier is
specified)
3) protected (accessible only to classes that subclass your
class directly within the current or different package)
4) public (accessible from any class)

Constructors are used for initializing new objects. Fields
are variables that provide the state of the class and its
objects, and methods are used to implement the
behavior of the class and its objects.
There are various types of classes that are used in real-
time applications such as nested classes, anonymous
classes, and lambda expressions.

Inner Class
Inner class refers to the class that is declared inside class
or interface which were mainly introduced, to sum up,
same logically relatable classes as Java is purely object-
oriented so bringing it closer to the real world. Now
geeks you must be wondering why they were
introduced?

There are certain advantages associated
with inner classes are as follows:
• Making code clean and readable.
• Private methods of the outer class can be accessed, so
bringing a new dimension and making it closer to the
real world.
• Optimizing the code module.

Types of Inner Classes
1.Nested Inner Class
2.Method Local Inner Classes
3.Static Nested Classes
4.Anonymous Inner Classes

Nested Inner Class
It can access any private instance variable of the outer class. Like
any other instance variable, we can have access modifier private,
protected, public, and default modifier. Like class, an interface can
also be nested and can have access specifiers.

Sample Nested Inner Class
Output:
In a nested class
method

Method Local Inner Class
Inner class can be declared within a method of an outer class
which we will be illustrating in the below example where Inner is
an inner class in outerMethod().

Output:
inside outerMethod
inside innerMethod

Static Nested Classes
Static nested classes are not technically inner classes. They are like
a static member of outer class.

Output
inside inner class Method
inside outerMethod

Anonymous Inner Classes
• Anonymous inner classes are declared without any name at all.
They are created in two ways.
• As a subclass of the specified type
• As an implementer of the specified interface

Output
i am in show method of super class
i am in Flavor1Demo class

Output:
In a nested class method

The benefits of using inner classes in Java
are:
• Encapsulation: Inner classes can access private variables and
methods of the outer class. This helps to achieve encapsulation and
improves code readability.
• Code Organization: Inner classes allow you to group related code
together in one place. This makes your code easier to understand
and maintain.
• Better Access Control: Inner classes can be declared as private,
which means that they can only be accessed within the outer class.
This provides better access control and improves code security.
• Callbacks: Inner classes are often used for implementing callbacks in
event-driven programming. They provide a convenient way to define
and implement a callback function within the context of the outer
class.

The benefits of using inner classes in
Java are:
• Polymorphism: Inner classes can be used to implement
polymorphism. You can define a class hierarchy within the outer
class and then create objects of the inner classes that implement
the different subclasses.
• Reduced Code Complexity: Inner classes can reduce the
complexity of your code by encapsulating complex logic and
data structures within the context of the outer class.
• Overall, the use of inner classes can lead to more modular,
maintainable, and flexible code.

Anonymous Inner Class
Nested Classes in Java is prerequisite required before adhering
forward to grasp about anonymous Inner class. It is an inner class
without a name and for which only a single object is created. An
anonymous inner class can be useful when making an instance of
an object with certain “extras” such as overriding methods of a
class or interface, without having to actually subclass a class.
Tip: Anonymous inner classes are useful in writing
implementation classes for listener interfaces in graphics
programming.

Objects
An object in Java is a basic unit of Object-Oriented
Programming and represents real-life entities. Objects
are the instances of a class that are created to use the
attributes and methods of a class. A typical Java program
creates many objects, which as you know, interact by
invoking methods

An object consists of :
1.State: It is represented by attributes of an object.
It also reflects the properties of an object.
2.Behavior: It is represented by the methods of an
object. It also reflects the response of an object
with other objects.
3.Identity: It gives a unique name to an object and
enables one object to interact with other objects.

Objects
Objects correspond to things found in the real world. For
example, a graphics program may have objects such as “circle”,
“square”, and “menu”. An online shopping system might have
objects such as “shopping cart”, “customer”, and “product”.

Declaring Objects (Also called instantiating
a class)
When an object of a class is created, the class is said to
be instantiated. All the instances share the attributes and the
behavior of the class. But the values of those attributes, i.e. the
state are unique for each object. A single class may have any
number of instances.

Initializing a Java object
The new operator instantiates a class by allocating memory for a
new object and returning a reference to that memory. The new
operator also invokes the class constructor.

Initializing a Java object
Output:
Hi my name is tuffy.
My breed, age and color are papillon,5,white

Object oriented programming CLASSES-AND-OBJECTS.pptx

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