Lecture-1
“Object Oriented Programming”
Introduction
• Object-Oriented Programming is a paradigm that provides many concepts,
such as inheritance, data binding, polymorphism, etc.
• Simula is considered the first object-oriented programming language. The
programming paradigm where everything is represented as an object is
known as a truly object-oriented programming language.
• Smalltalk is considered the first truly object-oriented programming language.
• The popular object-oriented languages are Java, C#, PHP, Python, C++, etc.
• The main aim of object-oriented programming is to implement real-world
entities, for example, object, classes, abstraction, inheritance, polymorphism,
etc.
OOPs (Object-Oriented Programming
System)
• Object means a real-world entity such as a pen, chair, table, computer, watch, etc.
• Object-Oriented Programming is a methodology or paradigm to design a program
using classes and objects. It simplifies software development and maintenance by
providing some concepts:
• Object
• Class
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation
Object
• Any entity that has state and behavior is known as an object. For example, a chair,
pen, table, keyboard, bike, etc. It can be physical or logical.
• An Object can be defined as an instance of a class. An object contains an address
and takes up some space in memory. Objects can communicate without knowing the
details of each other's data or code. The only necessary thing is the type of message
accepted and the type of response returned by the objects.
• Example: A dog is an object because it has states like color, name, breed, etc. as
well as behaviors like wagging the tail, barking, eating, etc.
Class
• Collection of objects is called class. It is a logical entity.
• A class can also be defined as a blueprint from which you can create an
individual object. Class doesn't consume any space.
•HumanBeing
•Male Female
Inheritance
• When one object acquires all the properties and behaviors of a parent object, it is known
as inheritance.
• It provides code reusability. It is used to achieve runtime polymorphism.
Polymorphism
• If one task is performed in different ways, it is known as polymorphism.
• For example: to convince the customer differently, to draw
something, for example, shape, triangle, rectangle, etc.
• In Java, we use method overloading and method overriding to achieve
polymorphism.
• Another example can be to speak something; for example, a cat speaks
meow, dog barks woof, etc.
Abstraction
• Hiding internal details and showing functionality is known as abstraction.
• For example phone call, we don't know the internal processing.
• In Java, we use abstract class and interface to achieve abstraction.
Encapsulation
• Binding (or wrapping) code and data together into a single unit are known as
encapsulation. For example, a capsule, it is wrapped with different medicines.
• A java class is the example of encapsulation. Java bean is the
fully encapsulated class because all the data members are private
here.
object in Java
• An entity that has state and behavior is known as an object e.g., chair, bike,
marker, pen, table, car, etc.
• It can be physical or logical (tangible and intangible).
• The example of an intangible object is the banking system.
• An object has three characteristics:
• State: represents the data (value) of an object.
• Behavior: represents the behavior (functionality) of an object such as deposit, withdraw, etc.
• Identity: An object identity is typically implemented via a unique ID. The value of the ID is not
visible to the external user. However, it is used internally by the JVM to identify each object uniquely.
For Example, Pen is an object. Its name is Reynolds; color is white, known as
its state. It is used to write, so writing is its behavior.
Class
• A class is a template or blueprint from which objects are created. So, an object is
the instance(result) of a class.
• A class is a group of objects which have common properties. It is a template
or blueprint from which objects are created. It is a logical entity. It can't be
physical.
• A class in Java can contain:
• Fields
• Methods
• Constructors
• Blocks
• Nested class and interface
Syntax to declare a class:
class <class_name>{
field;
method;
}
Instance variable in Java
• A variable which is created inside the class but outside the method is known
as an instance variable.
• Instance variable doesn't get memory at compile time. It gets memory at
runtime when an object or instance is created. That is why it is known as an
instance variable.
Method in Java
• In Java, a method is like a function which is used to expose the behavior of
an object.
• Code Reusability
• Code Optimization
new keyword in Java
• The new keyword is used to allocate memory at runtime.
• All objects get memory in Heap memory area.
22
