Agile%20Software%20Development

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Agile Software Development

• ??????

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??

• Introduction
• Agile Development
• Agile Design

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??

• Introduction
• Agile Development
• Agile Design

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Introduction

• Robert C. Martin Agile Software Development
  Principles, Patterns, and Practices, Prentice
  Hall (October 25, 2002)

Jolt Award 2003
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Introduction

• Robert C. Martin

Designing Object Oriented C Applications using
the Booch Method , 1995 Pattern Languages of
Program Design 3, 1997
More C Gems, 1999
Extreme Programming in Practice, 2003 UML for
Java Programmers ,2003
Uncle Bob
http//www.objectmentor.com
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Agile ??

• ??????????????????????????
• ????????????? -- practice
• ??????????????? -- principle
• ??????????? -- pattern
• ??????????,???????
  

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The Agile Alliance ????

• The Manifesto of the Agile Alliance ??????, 2001

http//www.agilealliance.org/

• We are uncovering better ways of developing
  software
• by doing it and helping others do it. Through
  this work
• we have come to value
• Individuals and interactions over processes and
  tools
• Working software over comprehensive documentation
• Customer collaboration over contract negotiation
• Responding to change over following a plan

Kent Beck, Alistair Cockburn, Robert C. Martin,
etc.
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??????

• ????????????
• ????????????????
• ??????????
• ??????????

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Principles

• ?????????????????????????????????
• ?????????,???????????????????????????
• ?????????????,????????????????,????????????

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Principles

• ?????????,????????????????????
• ?????????????????????????????,?????????????
• ?????,??????????????????,?????????

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Principles

• ????????????????
• ?????????????????????????????????????????????
• ???????????????????????

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Principles

• ?????????????????????
• ???????????????????
• ??????,????????????????????,????????????????

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Agile Processes

• SCRUM
• Crystal
• Feature Driven Development ????????
• Adaptive Software Development ???????
• eXtreme Programming (XP) ????

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??

• Introduction
• Agile Development
• Agile Design

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Agile Development

• Extreme Programming(XP,????) ?????????????,???????
  ?,????????,?????????????????????
• XP??????,????????????????????
• XP??team work??????,??,?????????????,????????????,
  ???????,???????????????

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Extreme Programming

• XP??4???
• ??(communication),XP???????????????????????
• ??(simplicity),XP????????????
• ??(feedback),????????,?????????????
• ??(courage),??????????????

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Extreme Programming

• XP??????????????,??????????????????,??????????????
  
• XP????????????,?????????????????,XP????????
• XP???????(???),???2-12???,XP???????????

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Practices of XP

• ????????
• ???? user stories
• ?????
• ????
• ????
• ????
• ???? pair programming

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Practices of XP

• ????????? Test-Driven Development
• ?????
• ????
• ????????
• ???????
• ???? planning game
• ?????
• ?? Refactoring
• ?? Metaphor???????????????

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??

• Introduction
• Agile Development
• Agile Design

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What is Design?

• After reviewing the software development life
  cycle as I understood it, I concluded that the
  only software documentation that actually seems
  to satisfy the criteria of an engineering design
  is the source code listings.
• -- Jack Reeves

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Design Smells

• Rigidity ??? ? ????
• Fragility ??? ? ????
• Immobility ??? ? ????
• Viscosity ??? ? ????
• Needless Complexity ???????
• Needless Repetition ??????
• Opacity ???

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The Copy Program

• Initial Design

void copy() int c while ((cRdKbd())!
EOF) WrtPrt(c)
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Requirement changes

• bool ptFlag false
• //remember to reset this flag
• void Copy()
• int c
• while ((c(ptFlag?RdPt() RdKbd())!EOF)
• WrtPrt(c)

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Requirement changes again!
bool ptFlag false bool punchFlag
false //remember to reset these flags void
Copy() int c while ((c(ptFlag?RdPt()
RdKbd())!EOF) punchFlag ? WrtPunch(c)
WrtPrt(c)
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Agile design of the copy example

• int RdKbd()
• void WrtPrt(int)
• const int EOF -1
• class Reader
• public virtual int read() 0
• class KeyboardReader public Reader
• public virtual int read() return RdKbd()
• KeyboardReader GdefaultReader
• void Copy(reader reader GdefaultReader)
• int c
• while ((creader.read()) ! EOF)
• WrtPrt(c)

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Agile developers

• Knew what to do because
• Detect the problem by following agile practices
• Diagnose the problem by applying design
  principles
• Solve the problem by applying the appropriate
  design pattern
• The interplay between these three aspects of
  software development is the act of design.

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A more complex example Multi-panel interactive
systems

• ??
• ????
• ??????
• ???????
• ??

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Multi-panel interactive systems

• ??
• ????
• ????(session)???????
• ????
• ??panel(???),??????(??),????,???,????????????????
  ???(????????????????)
• ????
• ??
• ????

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2019/7/10
Institute of Computer Software Nanjing University
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????

• ?????
• ?????
• ?????

?????????? (????)????? ?????
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A Simple-minded solution
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A Simple-minded solution

• ??
• Goto!
• ??
• ????????hardwired?????????
• ???????????
• ?????

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A functional, top-down solution

• ?,????goto,????????,??????? transition(state,choi
  ce)

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Top-down decomposition
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The top
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Critique
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Fragileness
???????
???????????
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object-oriented architecture

• Law of inversion
• If your routines exchange too many data, put your
  routines in your data.

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State as a class
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Use inheritance and deferred class
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The system? An ADT, not a main function
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2019/7/10
Institute of Computer Software Nanjing University
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??

• Focus on data abstraction
• Forget the main function of the system,
  resist the constant temptation to ask What does
  the system do?
• Law of inversion
• Realworldliness is not a significant difference
  between OO and other approaches what counts is
  how we model the world

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??

• Introduction
• Agile Development
• Agile Design
• design principles

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Design Principles

• SRP (The Single-Responsibility Principle) ??????
• OCP (The Open-Closed Principle) ??-????
• LSP (The Liskov Substitution Principle)
  Liskov????
• DIP (The Dependency-Inversion Principle) ??????
• ISP (The Interface-Segregation Principle) ??????

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SRP ??????

• A class should have only one reason to change.
  ??????,???????????????
• What is a Responsibility?
• A reason for change ???????????????????,??????,???
  ??????????
• An axis of change is an axis of change only if
  the changes actually occur. ??????????????????????
  ?

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Example
??????
????
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Example applying SRP
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??????
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Example SRP violation

• interface Modem
• public void dial (String pno)
• public void hangup()
• public void send (char c)
• public char recv()

connection management
data communication
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Example

• Separated modem interface

????????????????????????,?????????!
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OCP ??-????

• Software entities (classes, modules, functions,
  etc.) should be open for extension, but closed
  for modification. ????(????????)????????,????????
• OCP is the heart of OO design!

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OCP Description

• Two primary attributes
• Open for extension the behavior of the module
  can be extended
• Closed for modification extending the behavior
  of a module does not result in changes to the
  source or binary code of the module.
• ??????,???
• Is it possible?

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Abstraction is the key!
Client is neither open nor closed
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Strategy Pattern
Client is both open and closed
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Template Method Pattern
A clear separation of generic functionality from
the detailed implementation of that functionality
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Shape????

• ???????

--------drawAllShape.cc--- typedef struct Shape
ShapePointer void DrawAllShapes(ShapePointer
list, int n) int i for (i0iltni)
struct Shape slisti switch
(s-gtitsType) case square
DrawSquare((struct Square)s) break
case circle DrawSquare((struct Circle)s)
break
--------shape.h---------- enum ShapeTypecircle,sq
uare struct Shape ShapeType
itsType --------circle.h--------- struct
Circle ShapeType itsType double itsRadius
Point itsCenter --------square.h--------- str
uct Square ShapeType itsType double
itsSide Point itsTopLeft
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??OCP

• OOD????

class Shape public virtual void Draw()
const0 class Squarepublic Shape
public virtual void Draw() const class
Circlepublic Shape public virtual void
Draw() const void DrawAllShapes(vectorltShape
gt list) vectorltShapegtiterator I for
(ilist.begin()i!list.end()i)
(i)-gtDraw()
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??100??!

• ???????????????????,???
• ?????????,?????????????!

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Heuristics

• OCP????????????!
• ?????????????
• ??OOPL??????OCP
• ????????????
• 100??????,?????????????
• ????????????????????,??????????????????

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LSP Liskov????
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LSP Liskov????

• Subtypes must be substitutable for their base
  types. ?????????????????
• If for each object o1 of type S there is an
  object o2 of type T such that for all programs P
  defined in terms of T, the behavior of P is
  unchanged when o1 is substituted for o2 then S is
  a subtype of T. Liskov88 ??????S???o1,???????T??
  ?o2,???????T?????P?,?o1??o2?,??P??????,?S?T?????

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LSP Violation (I)
RTTI(???????)

• struct Shape
• enum ShapeType square, circle itsType
• Shape(ShapeType t)itsType(t)
• struct Circle public Shape
• Circle()Shape(circle)
• void Draw() const
• struct Square public Shape
• Square()Shape(square)
• void Draw() const

void DrawShape(const Shape s ) if(s.itsType
Shapesquare) static_castltconst
Squaregt(s).draw() else if (s.itsType
Shapecircle) static_castltconst
Circlegt(s).draw()
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LSP Violation (II)
class Rectangle public void
SetWidth(double w) itsWidthw void
SetHeight(double h) itsHeighth
private double itsWidth double
itsHeight
IS-A Relationship
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LSP Violation (II)

• void SquareSetWidth(double w)
• RectangleSetWidth(w)
• RectangleSetHeight(w)
• void SquareSetHeight(double w)
• RectangleSetWidth(w)
• RectangleSetHeight(w)

void f (Rectangle r) r.SetWidth(32) //call
RectangleSetWidth
Square Violated!
Square
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LSP Violation (II)
Are Rectangle and Square self-consistent?
class Rectangle public virtual void
SetWidth(double w) itsWidthw virtual void
SetHeight(double h) itsHeighth
private double itsWidth double
itsHeight
Square
void g (Rectangle r) r.SetWidth(5)
r.SetHeight(4) assert(r.Area()20)
True or false?
Violated!
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The real problem

• Validity is not intrinsic! ?????????
• ????????????????????
• IS-A is about Behavior
• Behaviorally, a Square is not a Rectangle.
• Recall DbC principle about inheritance
• Precondition ??Postcondition ??

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The real problem

• RectangleSetWidth(double w)?????
• Postcond (itsWidthw)(itsHeightold.itsHeight
  )
• ??SquareSetWidth(double w)???????
• ??????????????????

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Heuristics and Conventions

• Violation 1
• Degenerate functions in derivatives ?????????
• Violation 2
• Throwing exceptions from derivatives ?????????

public class Base public void f() /some
code/ Public class Derived extends Base
public void f()
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LSP

• One of the enablers of the OCP?
• LSP??OCP????????????
• It is the substitutability of subtypes that
  allows a module, expressed in terms of a base
  type, to be extensible without modification.
  ?????????????????????????????????????

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DIP ??????

• High level modules should not depend on low-level
  modules. Both should depend on abstractions.
  ??????????????,???????????
• Abstractions should not depend on details.
  Details should depend on abstractions.
  ??????????,??????????
• Inversion ??????????

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Laying

• Booch all well structured OO architectures
  have clearly defined layers, with each layer
  providing some coherent set of services through a
  well-defined and controlled interface.

Unfortunate!
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Laying
Hollywood principle dont call us, well call
you. ???????????????????????????

• Inverted layers

also an inversion of interface ownership
????????,??????????????
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Example
?
Button
Lamp
poll()
turnOn() turnOff()

• public class Button
• private Lamp itsLamp
• public void poll()
• if (/ some condition /)
• itsLamp.turnOn()

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Example
Button
ButtonServer
SwitchableDevice
poll()
turnOn() turnOff()
!
Lamp

• public class Button
• private ButtonServer bs
• public void poll()
• if (/ some condition /)
• bs.turnOn()

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Heuristic

• Depend on abstractions ?????
• ????????????????????????????????
• According to it
• ???????????????????????
• ?????????????
• ??????????????????????????
• ????????????,??String

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DIP

• ???????????????????????
• ?????????????,??????????,???????????
• DIP?????OO???????????????????????????????????????

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ISP ??????

• Clients should not be forced to depend on methods
  that they do not use. ??????????????????
• Deals with the disadvantage of fat interfaces
  whose interfaces are not cohesive. ???????????????

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Example
common door!
class Timer public void Register
(int timeout, TimeClient client )

• class Door
• public
• virtual void Lock() 0
• virtual void Unlock() 0
• virtual bool IsDoorOpen() 0

class TimerClient public virtual
void TimeOut () 0
How about a timed door?
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Interface Pollution
But not all varieties of Door need timing!
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Separate Interfaces

• Solution 1 adapter ????????

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Separate Interfaces

• class TimedDoor public Door
• public virtual void DoorTimeOut(int
  timeoutId)
• Class DoorTimerAdapter public TimeClient
• pubic
• DoorTimerAdapter(TimedDoor theDoor)
  itsTimedDoor(theDoor)
• virtual void TimeOut(int timeoutId)
• itsTimedDoor.DoorTimeOut(timeoutId)
• private
• TimedDoor istTimedDoor

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Separate Interfaces

• Solution 2 multiple inheritance

class TimedDoor public Door, public
TimerClient public virtual void TimeOut(int
timeoutId)
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Heuristic

• ????????????????????!
• ???????????????????????
• ?????,???!

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Design Principles

• SRP (The Single-Responsibility Principle) ??????
• OCP (The Open-Closed Principle) ??-????
• LSP (The Liskov Substitution Principle)
  Liskov????
• DIP (The Dependency-Inversion Principle) ??????
• ISP (The Interface-Segregation Principle) ??????

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How to design Packages?

• ?????????????????
• ????????????????????
• ??????????(????)????????????(????)?
• ?????????C?Java????????
• ?????,????????????

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?????????

• REP (The Reuse-Release Equivalence
  Principle),????????,?????????????
• CRP (The Common-Reuse Principle),??????,??????????
  ???????
• CCP (The Common-Closure Principle),??????,????????
  ?????????????????

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REP

• ?????????,???????????????-- ????????
• REP??,????????(granule of reuse)???????(granule
  of release)????????????????????????
• ??????????????!
• ??????????,??????????????????????????????????????

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CRP

• ????????????????,???????????,?????????????
• ??????????????????
• ??????????????????????
• jar??????

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CCP

• ??????????????????????????????????????,???????????
  ???,???????????????
• ???SRP,OCP
• ????????????????????????????

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??????????

• ADP (The Acyclic-Dependencies Principle),??????,??
  ??????????????
• SDP (The Stable-Dependencies Principle),??????,???
  ?????????
• SAP (The Stable-Abstractions Principle),??????,???
  ??????????????

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ADP

• ?????
• ????
• ?????
• DAG

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ADP

• ????????
• ??MyTasks
• ??MyDialogs

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?????

• ??1 ????????

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?????

• ??2 ????????????,????????????

Jitter???
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Heuristic

• ????????????
• ????????????????????
• ?????????????????????????,??,????????????????

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SDP

• ?????????
• ???????,?????????,?????????????????,??,???????????
  ?

???
??
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?????

• (Ca)???????????????????????????
• (Ce)???????????????????????????
• ????I 0,1
• I0 ???
• I1 ????
• SDP??????I??????????????I???(?I??????????????)

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?????
Pa
Pb
q
r
s
Pc
Pd
t
u
v
Pc Ca3, Ce1, I1/4
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?? vs. ???

• ?????????????

???HOW TO?
i1
i1
i0
??????
???SDP
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?? vs. ???
DIP
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SAP

• ????????????????
• ?????????????,????????????????
• ?????????????,???????????????????????

?????????????!
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Remember

• As with all principles, care must be taken not to
  overdo it.

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?? (????????)

• ?????????????????
• ??JDK?Collection??????,?????????????????????????