UNIT I INTRODUCTION TO OOP AND JAVA FUNDAMENTALS 10
Object Oriented Programming - Abstraction – objects and classes - Encapsulation- Inheritance -
Polymorphism- OOP in Java – Characteristics of Java – The Java Environment - Java Source File -Structure
– Compilation. Fundamental Programming Structures in Java – Defining classes in Java – constructors,
methods -access specifiers - static members -Comments, Data Types, Variables, Operators, Control Flow,
Arrays , Packages - JavaDoc comments.
OOPs (Object Oriented Programming System)
Object means a real word entity such as pen, chair, table etc. Object-Oriented Programming is
a methodology or paradigm to design a program using classes and objects. It simplifies the
software development and maintenance by providing some concepts:
o Object
o Class
o Inheritance
o Polymorphism
o Abstraction
o Encapsulation
In this page, we will learn about java objects and classes. In object-oriented programming technique, we
design a program using objects and classes.
Object is the physical as well as logical entity whereas class is the logical entity only.
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
intangible object is banking system.
An object has three characteristics:
o state: represents data (value) of an object.
o behavior: represents the behavior (functionality) of an object such as deposit,
withdraw etc.
o identity: Object identity is typically implemented via a unique ID. The value of the
ID is not visible to the external user. But, it is used internally by the JVM to identify
each object uniquely.
Class in Java
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:
, o fields
o methods
o constructors
o blocks
o nested class and interface
Inheritance in Java
Inheritance in java is a mechanism in which one object acquires all the properties and
behaviors of parent object. It is an important part of OOPs (Object Oriented programming
system).
The idea behind inheritance in java is that you can create new classes that are built upon
existing classes. When you inherit from an existing class, you can reuse methods and fields
of parent class. Moreover, you can add new methods and fields in your current class also.
Types of inheritance in java
On the basis of class, there can be three types of inheritance in java: single, multilevel and
hierarchical.
In java programming, multiple and hybrid inheritance is supported through interface only.
We will learn about interfaces later.
, Polymorphism in Java
Polymorphism in java is a concept by which we can perform a single action by different
ways. Polymorphism is derived from 2 greek words: poly and morphs. The word "poly"
means many and "morphs" means forms. So polymorphism means many forms.
There are two types of polymorphism in java: compile time polymorphism and runtime
polymorphism. We can perform polymorphism in java by method overloading and method
overriding.
If you overload static method in java, it is the example of compile time polymorphism. Here,
we will focus on runtime polymorphism in java.
Runtime Polymorphism in Java
Runtime polymorphism or Dynamic Method Dispatch is a process in which a call to an
overridden method is resolved at runtime rather than compile-time.
In this process, an overridden method is called through the reference variable of a
superclass. The determination of the method to be called is based on the object being
referred to by the reference variable.
Method Overloading in Java
If a class has multiple methods having same name but different in parameters, it is known
as Method Overloading.
If we have to perform only one operation, having same name of the methods increases the
readability of the program.
Suppose you have to perform addition of the given numbers but there can be any number
of arguments, if you write the method such as a(int,int) for two parameters, and
b(int,int,int) for three parameters then it may be difficult for you as well as other
programmers to understand the behavior of the method because its name differs.
Object Oriented Programming - Abstraction – objects and classes - Encapsulation- Inheritance -
Polymorphism- OOP in Java – Characteristics of Java – The Java Environment - Java Source File -Structure
– Compilation. Fundamental Programming Structures in Java – Defining classes in Java – constructors,
methods -access specifiers - static members -Comments, Data Types, Variables, Operators, Control Flow,
Arrays , Packages - JavaDoc comments.
OOPs (Object Oriented Programming System)
Object means a real word entity such as pen, chair, table etc. Object-Oriented Programming is
a methodology or paradigm to design a program using classes and objects. It simplifies the
software development and maintenance by providing some concepts:
o Object
o Class
o Inheritance
o Polymorphism
o Abstraction
o Encapsulation
In this page, we will learn about java objects and classes. In object-oriented programming technique, we
design a program using objects and classes.
Object is the physical as well as logical entity whereas class is the logical entity only.
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
intangible object is banking system.
An object has three characteristics:
o state: represents data (value) of an object.
o behavior: represents the behavior (functionality) of an object such as deposit,
withdraw etc.
o identity: Object identity is typically implemented via a unique ID. The value of the
ID is not visible to the external user. But, it is used internally by the JVM to identify
each object uniquely.
Class in Java
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:
, o fields
o methods
o constructors
o blocks
o nested class and interface
Inheritance in Java
Inheritance in java is a mechanism in which one object acquires all the properties and
behaviors of parent object. It is an important part of OOPs (Object Oriented programming
system).
The idea behind inheritance in java is that you can create new classes that are built upon
existing classes. When you inherit from an existing class, you can reuse methods and fields
of parent class. Moreover, you can add new methods and fields in your current class also.
Types of inheritance in java
On the basis of class, there can be three types of inheritance in java: single, multilevel and
hierarchical.
In java programming, multiple and hybrid inheritance is supported through interface only.
We will learn about interfaces later.
, Polymorphism in Java
Polymorphism in java is a concept by which we can perform a single action by different
ways. Polymorphism is derived from 2 greek words: poly and morphs. The word "poly"
means many and "morphs" means forms. So polymorphism means many forms.
There are two types of polymorphism in java: compile time polymorphism and runtime
polymorphism. We can perform polymorphism in java by method overloading and method
overriding.
If you overload static method in java, it is the example of compile time polymorphism. Here,
we will focus on runtime polymorphism in java.
Runtime Polymorphism in Java
Runtime polymorphism or Dynamic Method Dispatch is a process in which a call to an
overridden method is resolved at runtime rather than compile-time.
In this process, an overridden method is called through the reference variable of a
superclass. The determination of the method to be called is based on the object being
referred to by the reference variable.
Method Overloading in Java
If a class has multiple methods having same name but different in parameters, it is known
as Method Overloading.
If we have to perform only one operation, having same name of the methods increases the
readability of the program.
Suppose you have to perform addition of the given numbers but there can be any number
of arguments, if you write the method such as a(int,int) for two parameters, and
b(int,int,int) for three parameters then it may be difficult for you as well as other
programmers to understand the behavior of the method because its name differs.
