Martin Q. Zhao
9/20/2013
THE DAO OF OBJECT-ORIENTATION
TOPICS
Dao De Jing (Tao-Te Ching) & Lao Zi (Lao Tzu)
 Dao of Programing
 Building the Virtual World
 OOAD Principles in Dao De Jing

道德经(DaoDe Jing) & 老子(Lao Tzu)
郭店竹简 (GuoDian Bamboo Slips)
A World With 10,000 Objects
Existence
Nothingness,
emptiness
Name,
concept
Subtlety
The Tao
Beginning
The Tao
that can be
expressed
in words is
not the true
and eternal
Tao… (Tao:1)
10,000 things,
objects
Heaven &
earth, the
world
Dao Of Programming???
Info Books (September 1986)
Addison-Wesley Professional;
1 edition (July 22, 2004)
M & T Books
(December 1990)
Patrick Burns
Hayden Books; 2 Pap/Dskt edition (July 1994) (December 16, 2012)
Computing & Computer Programs

The discipline of computing is …
the systematic study of algorithmic processes that
describe and transform information: their theory,
analysis, design, efficiency, implementation, and
application. The fundamental question underlying all of
computing is, ‘What can be (efficiently) automated?’

Computer programs: sets of instructions written
in programming languages that automate Real
World information transformation processes
 Develop
World”
a software system is like building a “Virtual
How To Structure Programs?

Software systems can be boiled down to
 Systems:
the solution as a whole (virtual worlds)
 Programs:
organizational units of code (or the VW)
 Procedures:
sequences of instructions as a unit
 Statements:
instructions
 Expressions:
meaningful combo of tokens
 Tokens:
variables, constants, operators, punctuations
Procedural Vs. O-O Approaches

Procedural approach,
aka Structured
Programming (mid-1960’s)
top

OO approach (since 1980’s)


Procedures
Or ways to
process data
Data
Data and algorithms go
together (in an object)
No “top” unit
Real World & Virtual World

Real World (aka
Problem Domain)

Consists of objects (or
entities)
Employee ID
Name
Phone
Brand
Category
Price
Name
Address
Payment method

Virtual World (aka
Solution Domain)


Specs of classes
Objects created at
runtime (when VW is alive)
At The Very Beginning…
Now let’s focus on the Virtual World
 Building the VW involves defining the classes
that will be used to create objects at runtime

有物混成，先天地生。
S/W SystemThe Tao
VW
寂兮寥兮，独立而不改。
周行而不殆，可以为天地母。
吾不知其名，强字之为道 ，There is a thing integratedly formed
强为之名曰大 。
And born earlier than Heaven and Earth.
Objects
Silent and empty, it relies on nothing,
Moving around forever.
We may regard it as the mother of all things
I don’t know its name, so I name it as Tao,
And further name it as Great. (Tao:25)
A Simplest Example
class Dummy
A {} {}
What is the simplest Java class?
 Can it be used to create any object?

Inheritance
Add it here
class DummyTest {
public static void main (String[] x) {
Dummy d = new Dummy();
}
extends Object
}

But can this object be used?
Add it here
System.out.println(d);

What happens behind the scene?
 Class
Object is the “mother” of all Java classes
What Does An Object Have?

An object has a type
Abstraction
 Object
: instance of a class, created at runtime
 Class : template of all objects of the same type

An object has an identity
 Two
labs in CSB may look the same, but each is a
unique entity

(Classes of) objects have their responsibilities:
o:Order
they need to
 Know
some information
 perform some operations
-orderId=101
-orderDate=1/1/11
+calOrderTotal()
…
How To Identify Classes & Assign Responsibilities?

One easy choice
 Just
use one GOD CLASS, which
R. Martin (2003) Prentice Hall
UML for Java Programmers
 Knows everything and can do everything

But that is not OO, which tends to
 Partition
system into many classes around RW
concepts, and
 Distribute intelligence/behavior evenly among them
天地不仁，以万物为刍狗…
Heaven and Earth have no favorite,
They deem all objects as equally common.
(Tao:5)
Keep It Simple
Keep being simple in nature and mind (见素抱
朴)  close to Tao  to avoid “an early end”
(不道早已:whatever goes against Tao will come to an early end)
 Keeping classes’ responsibilities
simple (or cohesive), helps reuse
& improve system maintainability

五色令人目盲；
五音令人耳聋；
The five colors make man blind;
The five sounds make man deaf;
五味令人口爽；
The five tastes make man lose his sense of taste;
驰聘畋猎，令人心发狂； Riding and hunting make man wild w/ excitement;
难得之货，令人行妨。 Rare goods goad man into stealing ... (Tao:12)
The Single Responsibility Principle

Instead of using all-purpose
objects, objects with a single
responsibility are preferred
Maintainability
R. Martin (2002) Prentice Hall
Agile Software Development
How Do I Know What Objects To Use?

Focus on the three types of objects
Tao
Tao begets
begets the
the One;
One;
The
The One
One consists
begets the
of Two
Two;in opposition
(the
The Yin
Twoand
begets
Yang);
the Three;
The
The two
Three
begets
begets
the10,000
Three; things.
All
(Te:42)
things connote the Yin and Yang.
(Te:42)
道生一，
一生二，
二生三，
三生万物。
(Cont’d on
next slide)
A VW With 10,000 Objects
CustomerEntity
Customer
CustomerForm
OrderControl
Actors
OrderEntity
SalesRep
SalesRepForm
OrderFulfillControl
ProductEntity
System Boundary
Analysis Class Stereotypes
Entity classes
usually represent
a domain-specific
situation or RW
object
Need to be saved
between sessions
Control classes
represent a
workflow, control,
or calculation
process
Boundary classes
are used to model
interaction between
the system and its
actors.
Jacobson, Booch, & Rambaugh (1999) Addison-Wesley
The Unified Software Development Process
Interactions Of Objects In The VW
Each object can do only one thing
 To fulfill its responsibility, an object can ask for
help from (aka collaborate with) another object
 Object collaboration is done by message
changeGears(5)
passing
myBike:Bike
me:Rider
 A message has

A
recipient
 An operation requested
 Additional information to carry out the operation
Java online tutorials: What Is an Object?
http://docs.oracle.com/javase/tutorial/java/concepts/object.html
Let The Server Do It
Choose to (take)
no action

One way to get help is to delegate
 The
Delegation
client object will “do nothing” (无为) itself
(Take) no action
 It delegates reuses the service from the “server”
object that implements it
 The client and server roles are specific for each
episode
server
client
objectA
objectB
client
server
Contract Between Objects

Encapsulation
The Design by Contract approach prescribes
 software
designers should define formal, precise
and verifiable interface specifications for software
components (i.e. classes), including
 Services/operations to provide, and
 For each operation, to specify
 Preconditions:
need to be true before it’s carried out;
 Postconditions: need to be true after it’s completed, and
 Invariants: need to hold true during the object’s life time
 These
specifications are referred to as "contracts".
Mitchell & McKim (2002) Addison-Wesley
Design by Contract, by example
The Usefulness Of Nothingness
Thirty spokes share one hub.
It is just the space (the Nothingness) between
them that makes a cart function as a cart. (Tao:11)
Interfaces, Abstract Classes, & Patterns



An abstract class may have some operations not
implemented (in another word, left empty)
An interface is a purely abstract class in which no
operations may be implemented
Reusability
Interfaces and abstract classes are commonly used in
design patterns [A design] pattern describes a problem
Alexander, Christopher (1977)
Oxford University Press.
A Pattern Language: Towns,
Buildings, Construction.
that occurs over and over again in our
environment, and then describes the core
of the solution to that problem, in such a
way that you can use this solution a million
times over, without ever doing it the same
way twice.
A Common Pattern: Arch
A Software Pattern: Composite
Make Parts(components) Into A Unit (Composite)
Client
Composite
pattern
Another Software Pattern: Façade
Hide Parts Using A Façade(MyGameTank)
Client
Façade
pattern
Decouple Client W/ Concrete Tank
Abs. Factory
pattern
Adding A New Tank Type W/ Ease
E1T1TankFactory
+createTank():E1T1Tank
+createShell():E1T1TankShell
E1T1Tank
E1T1TankShell
Handling User Input W/ KeyListener
Command
pattern
A hook method in
the Java AWT API
<<interface>>
KeyListener
+keyPressed(e:KeyEvent)
+keyReleased(e:KeyEvent)
+keyTyped(e:KeyEvent)
MyGameFrame
MyGamePanel
AbstractTank
KeyHandler
+keyPressed(e:KeyEvent)
+keyReleased(e:KeyEvent)
+keyTyped(e:KeyEvent)
Software Frameworks
Another way to reuse is to use frameworks
 A framework provides collections of
interfaces, abstract classes, and concrete
classes
 Sample frameworks in Java
 Swing, AWT: from GUI (boundary objects)
 JDBC/IO/NIO: for saving entity objects to
DB or files
 Collections: for managing entity objects

The Strength Of Softness
天下莫柔弱于水，而攻坚强者莫
之能胜，以其无以易之。
Nothing in the world is more supple than water,
Yet nothing is more powerful than water
In attacking hard and strong. (Te:78)
The perfect
goodness is
like water.
(Tao:8)
天下之至柔，驰骋天下之至坚。
The most supple in the world,
Can go through the hardest in the world. (Te:43)
Software Is Soft

Favor flexibility over rigidity
人之生也柔弱，其死也坚强。
万物草木之生也柔脆，其死也枯槁。
故坚强者死之徒，柔弱者生之徒。
……
强大处下，柔弱处上。
While alive, a person’s body is supple; when
dead, it becomes rigid.
While alive, grass and trees are supple; when
dead, they become dry and stiff.
Thus the hard and strong is of the dying sort;
the supple and weak is of the living sort.
……
Thus the strong and big is inferior to the weak
and supple. (Te:76)
Design Smells: The Odors Of Rotting Software
Rigidity
 Fragility
 Immobility
 Viscosity
 Needless complexity
 Needless repetition
 Opacity

R. Martin (2003) Prentice Hall
UML for Java Programmers
五色土(Earth In 5 Colors)