Lecture 4
- 1. OOPs with C++ Lecture 4
- 2. What is Object Oriented Programming? An object is like a black box. The internal details are hidden. Identifying objects and assigning responsibilities to these objects. Objects communicate to other objects by sending messages . Messages are received by the methods of an object
- 3. The two steps of Object Oriented Programming Making Classes: Creating, extending or reusing abstract data types. Making Objects interact: Creating objects from abstract data types and defining their relationships.
- 4. Example: The Creature class class Creature { private: int yearOfBirth; public: void setYearOfBirth(year) { yearOfBirth = year; } int getYearOfBirth() { return yearOfBirth; } };
- 5. Example: The Creature class class Creature { private: int yearOfBirth; public: void setYearOfBirth(year); int getYearOfBirth(); }; void Creature::setYearOfBirth { yearOfBirth = year; } int Creature::getYearOfBirth() { return yearOfBirth; } Note that unless the methods are very short, declaration and implementation is usually separated. The declaration goes into a header file (.h), the implementation in a .cpp file.
- 6. Classes & Objects What may be different for all objects in a class, and what remains the same? All the objects in a class may have different attribute values (state data), but their allowed behaviours are all the same. So a class is a blueprint for objects
- 7. Objects & Classes A class is defined by: A Unique Name Attributes Methods An object is defined by: Identity State Behaviour
- 8. Instantiating Objects An object is instantiated just like any other data type: int x; char y; Creature z; Declaring z of type ‘creature’ means we have generated an object with the attributes and methods of the class.
- 9. Multiple Objects Of course we can create many objects of the same class: Creature myDog; Creature theMilkman; Creature myBestFriend; Creates three objects.
- 10. Sending Messages / Calling Methods. A message is send to an object by calling a method of this object. Use the . (dot) for calling a method of an object. int k; k = theMilkman.getYearOfBirth(); myDog.setYearOfBirth(1998); Messages are sent to my dog and the milkman.
- 11. Back to the Instantiation... An object is instantiated just like any other data type: int x; char y; Creature z; Here the “default constructor” of the Creature class is automatically called. If we don’t like this we can specify constructors explicitly!
- 12. End