01_Object Oriented Programming

Object

What’s an object

• Object = Entity
• Object may be
  • Visible or
  • invisible
• Object is variable in programming languages.

对象在编程语言中，以变量的形式出现。

Objects = Attributes + Services

• Data: the properies or status
• Operations: the functions

Mapping

• From the problem space to the solution one.

写程序的过程=用计算机程序描述问题+用计算机程序解决问题。
这是一种从 问题空间->解决空间 的映射

What’s object-oriented

• A way to organize
  • Designs
  • Implementations
• Objects, not control or data flow, are the primary focus of the design and implementation.
• To focus on things, not operations

Object Oriented Programming

这节主要讲OOP的基本理念

• Objects send and receive messages(objects do things!)

send messages

• Message are
  • Composed by the sender
  • Interpreted by the receiver
  • Implemented by methods
• Messages
  • May cause receiver to change state
  • May return results

消息以函数形式传递，消息可能会改变接受者状态（也可以返回结果）

class & object

The fish is fish. The bird is bird. (Aristotle)

• Objects (cat)
  • Represent things, events, or concepts
  • Respond to messages at run-time
• Classes (cat class)
  • Define properties of instances
  • Act like types in C++

OOP Characteristics

1. Everything is an object
2. A program is a bunch of objects telling each other what to do by sending messages.

   这里是 what to do 不是 how to do

3. Each object has its own memory made up of other object.

   每个对象都有由其他对象组成的自己的内存

4. Every object has a type
5. All objects of a particular type can receive the same messages.

interface

• The interface is the way it receives messages.
• It is defined in the class the object belong to.

functions of the interface

• Commnication
• Protection

  接口保护对象内部状态

The Hidden Implementation

• Inner part of an object, data members to present its state, and the actions it takes when messages is rcvd is hidden.
• Class creators vs. Client programmers
  • Keep client programmers’ hands off portions they should not touch.
  • Allow the class without worrying about how it will affect the client programmers.