[工学]面向对象程序设计.ppt

Chapter 13 Object-oriented programming 面向对象程序设计 13.1 Introduction object-oriented design/ programming A software design/programming method that models the characteristics of abstract or real objects using classes and objects. Object-Oriented Programming (OOP) Inheritance继承性 - form of software reusability重用性 New classes created from existing ones Absorb attributes and behaivors, and add in their own Override methods - redefine inherited methods Subclass inherits from superclass Direct superclass - subclass explicitly inherits Indirect superclass - subclass inherits from two or more levels up the class heirarchy Polymorphism多态性 Write programs in a general fashion to handle a wide variety of classes Abstraction抽象 - seeing the big picture Inheritance example A rectangle is a quadrilateral.四边形 Rectangle is a specific type of quadrilateral Quadrilateral is the superclass, rectangle is the subclass Incorrect to say quadrilateral is a rectangle Naming can be confusing because subclass has more features than superclass Subclass more specific than superclass Every subclass is an object of its superclass, but not vice-versa Form tree-like hierarchal structures Create a hierarchy for class Shape (next slide) Using inheritance Use keyword extends class TwoDimensionalShape extends Shape{ ... } private members of superclass not directly accessible to subclass All other variables keep their member access What Is an Object? Objects are key to understanding object-oriented technology. You can look around you now and see many examples of real-world objects: your dog, your desk, your television set, your bicycle. These real-world objects share two characteristics: They all have state and behavior. For example, dogs have state (name, color, breed, hungry) and behavior (barking, fetching, and wagging tail). Software objects are modeled after real-world objects in that they too have state and behavior. A software object maintains its state in one or more variables . A variable