Lecture02

Lecture02

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  Lecture 02 Fundamentals of Object-Oriented Programming
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  What Are Objects? Softwareobjects model real-world objects or abstract concepts. dog, bicycle, queue Real-world objects have states and behaviors. Dogs' states: name, color, breed, hungry Dogs' behaviors: barking, fetching How do software objects implement real-world objects? Use variables/data to implement states. Use methods/functions to implement behaviors. An object is a software bundle of variables and related methods.
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  Software Object Visual Representation Instance Variables Vs Instance Methods
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  Software Bicycle Visual Representation
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  What Are Classes? •A class is a blueprint or prototype defining the variables and methods common to all objects of a certain kind. • An object is an instance of a certain class. • After you have created a class, you must create an instance of it before you can use. • Class variables and class methods.
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  What Are Messages? Softwareobjects interact and communicate with each other by sending messages to each other.
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  Components Of AMessage The object to whom the message is addressed (YourBicycle) The name of the method to perform (changeGears) Any parameters needed by the method (lowerGear)
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  O-O Principles • Abstraction- take only important information • Encapsulation - hiding or combine data and operations on data in a single unit. • Inheritance - create new objects from existing objects. • Polymorphism-the ability to use the same expression to denote different operations.
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  Encapsulation • The objects'variables make up the center of the object. • Methods surround and hide the object's center from other objects. • Benefit of encapsulation: Modularity & Information Hiding. • For implementation or efficiency reasons, an object may wish to expose some of its variables or hide some of its methods.
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  Inheritance • Inheritance allowsclasses to be defined in terms of other classes. • Each subclass inherits variables and methods from its superclass. • Subclasses can add variables and methods to the ones they inherit from the superclass. • Subclasses can also override inherited methods and provide specialized implementations for those methods.
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  Class Hierarchy (Inheritance Hierarchy) Superclass vs Subclass. Base Class vs Derived Class.
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  Polymorphism and Overloading •Polymorphism allows the use of operators or functions in different ways, depending on the data they are operating on. • When an existing operator (eg. + or =) is given the capability to operate on a new data type, it is said to be overloaded. • Overloading is a kind of polymorphism; it is also an important feature of OOP. • Example of operator overloading and polymorphism) • the + operator know how to treat an integer and a float differently.
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  Benefits of OOP Reusability • Once written, created, and debugged, a class can be distributed to other programmers for use in their own programs. • Reusability facilitates component-based software design and implementation. • A programmer can also take an existing class and, without modifying it, add additional features and capabilities to it.
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  Benefits of OOP Creating New Data Types • Objects and classes give the programmer a convenient way to construct new data types. • Many features of C++ are intended to facilitate the creation of new data types. • The ability to create new data types leads to extensible languages and programs. • In C++, new data types can be built on top of existing (system or user-defined) data types.
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  C++ Program Structure #include <iostream.h> Header files preprocessor statements class Data int main( ) // VOID Members { ….. and Member { } Functions main( ) Variable cout << “Welcome to C++”; { …… declarations & return 0; valid C++ } statements }
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  Example 2 #include <iostream.h> Sum = a + b + c; int main ( ) cout << “ the sum is “<< sum; { int a , b, c, sum =0; cout << “ enter a value “<<endl; OTHER DATA TYPES cin >> a; Char int cout << “ enter b value “<<endl; long int float cin >> b; double cout << “ enter c value “<<endl; cin >> c;
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  Input / Output Cout- used for printing out the output Syntax : Cout << “Message if needed”<< variablename; << is called the insertion operator. Cin - used for getting a input from the keyboard Syntax: Cin >> variable name; >> is called the extraction operator
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  Other Points Remark statement- it is a non executable statement used for documentation // or /* statements */ escape sequences: n - new line t - horizontal tab r - carriage return a - bell - back slash ” - double quotations