Module1 elementary concepts of objects and classes

QUICK REVISION GUIDE – THEORY PORTION MODULE ELEMENTARY CONCEPTS OF OBJECTS AND CLASSES Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer

TOPICS TO REVISE       class object abstraction encapsulation inheritance polymorphism Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

 Definition of a class in OOP  Definition of a class in the real world  Example of a classes and objects in the real world  Format of defining a class  Attributes required for defining a class  members of a class i) instance variable/member variable/data member / fields ii) class variable / static variable iii) constructor

OBJECT           definition of object in the real world Definition of object in OOP Example of an object in the real world with characteristics and behaviour Characteristics / state of an object Behaviiour of an object format of object declaration Format of object creation memory allocation of an object referencing members of a class using an object representing real world objects in object oriented programming Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

ABSTRACTION  Abstraction is the act of representing   essential features of a system without including the background details or explanations Example of abstraction in the real world Example of abstraction in OOP Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

ENCAPSULATION  The wrapping up of data and the related  functions into a single unit called class is known as encapsulation. Data hiding /Information hiding preventing unauthorized accessing of data from outside the class using the principle of encapsulation and private access modifier is called data hiding Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

INHERITANCE       Definition Need for Inheritance base class and derived class Different forms of inheritance - types of inheritance supported by java Use of key words extends and super Function overriding Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Definition  Inheritance is the process by which a class acquires the properties of another class. Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Advantages of inheritance  help us to express inheritance  relationship which ensures closeness with real-world models reusability of existing classes Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Base class and Derived class class A base class class B derived class  base class is the class from which properties are acquired. It is also called super class or parent class Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Base class and derived class class A base class class B  derived class derived class is the class that acquire properties from another class. It is also called sub class or child class or extended class Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Different forms of inheritance single inheritance class A class B A sub class inherits only from a base class Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Different forms of inheritance multilevel inheritance class A class B a sub class inherits from a class that itself inherits from another class class C Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Different forms of inheritance multiple inheritance class A class B class C a class is derived from two or more Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer base classes Applications Students

Different forms of inheritance hybrid inheritance class A class B class C class D a class acquires properties from another class through two or more paths Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Different forms of inheritance hierarchical inheritance class A class B class C class D a class has several sub classes Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Use of access modifiers in Inheritance  private members of a class can  be used only with in the class members of a class with default access can be used with in the class as well as in all the classes with in the same package Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Use of access modifiers in Inheritance  protected members of a class can  be used with in the class, in a class of the same package as well as in a sub class. The sub class may be in the same package or in a different package public members of a class can be used everywhere Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

private access modifier yes no no no no default access modifier yes yes yes no no protected access modifier public access modifier yes yes yes yes no yes yes yes yes yes 19 can be accessed with in the class can be accessed in a sub class of same package can be accessed in a class of same package can be accessed in a sub class of a different can be accessed in a class of another access modifier of member variable / member function

POLYMORPHISM   Polymorphism comes from Greek meaning “many forms.” Polymorphism is the process by which the same message can be given to objects of different classes and each object responds to this message in a different manner depending on its class. Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

POLYMORPHISM     passing a message to an object is same as calling a function using an object. for e.g: String s1=s.substring(5,8); In the above statement we invoke the substring function of class string using the object s1. We can also say that we pass a message substring to the object s1 with the values 5 and 8 Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

POLYMORPHISM  Function overloading can be considered  as an example of polymorphism Binding - dynamic binding or late binding - static binding or early binding Prepared by Merson Mathew, St. Joseph’s School Bhagalpur for ICSE Computer Applications Students

Module1 elementary concepts of objects and classes

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