Essential OOP

今天無情無義地拋開 IS term project，向同學講述超濃縮的 OOP 核心概念。從 data abstraction 一路講到 polymorphism，可以感覺已經連成一氣了。（但我不知道有沒有表達出來 XD。）以下是我擬的大綱（防止偏離主幹），DBC 的 precodition / postcondition 實際講時跳過沒提。

1. data abstraction
 object-oriented paradigm ==> object-oriented decomposition
 What is an "object"? ==> behavior, responding to certain "messages"
 send an object a message ==> invoke that object's instance method
                              oms., public instance method
 interface: the general idea
            abstraction (Andrew Koenig: "Abstraction is selective ignorance.")
     ==> data abstraction, procedure abstraction
 interface (public members) vs. implementation (private members)
 encapsulation ==> why? enforcing abstraction, state maintenance
 Design by Contract (DBC): class invariants
 state constructing ==> constructor
 state destructing ==> garbage collector & explicit resourse release
                       (vs. destructor)
 Doug McIlroy: "Those types are not 'abstract', they are as real as int and float."

2. class extension (inheritance) & polymorphism
 perspective 1: program by difference
   a subclass object = a superclass subobject + the subclass part
     ==> a subclass constructor must invoke one of its superclass constructors
   Why member hiding?
   essentially an extension of data abstraction
 perspective 2: program to the interface
   inheritance <==> IsA relationship between subclass and superclass
                    oms., a substitutable relationship (LSP)
   reference type vs. actual type
   Why method overriding? the message model
   DBC: precoditions and postconditions of instance methods
     ==> access level raising, exception throws list, covariant return type
 polymorphism: the interface perspective & the object perspective

2.1 abstract classes and interfaces
 the superclass is just an abstract concept ==> no instantiation
   abstract classes are always used in class extension
   utility class ==> use a private constructor
 Java class = implementation
 Java interface ==> pure interface, no implementation
 multiple implementation of interfaces
   ==> the object has many forms, i.e., the object perspective of polymorphism
 JavaPL4e, p.131: "Any major class you expect to be extended, whether
   abstract or not, should be an implementation of an interface."
   ==> program to the interface, not to the implementation (class)

看似份量不多，但也講了五、六個小時。感覺不錯 :)。

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晚上要和 RMI、HTML、cookies 混戰了 XD。