Java

Web

Programming

Advanced

Week01

Dependency Injection

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Dependency

Dependency

Dependency in OO

Method Call

Object A

Object B

Object A

Object B

depends on

in Code

public class MovieLister { public List findAll() { ... } } public class MovieFinder { private MovieLister lister; public void moviesDirectedBy(String title) { List allMovies = lister.findAll(); ... } } Dependency

class Lecture Class Standard Grader Dependency C o d e Rev i ew

C o d e Rev i ew

class Lecture Class Standard Grader Dependency Class PassFail Grader

Coupling

= Coupling

Object A

Object B

Dependency

= Coupling

Object A

Object B

Dependency

Coupling

OO

Goal

= Coupling

Object A

Object B

Dependency

Tight Coupling?

class Lecture Class Standard Grader Dependency P ro bl e m

Class Dependency

P ro bl e m

class Lecture Class Standard Grader Dependency Class PassFail Grader Class

P ro bl e m

class Lecture Class Standard Grader Dependency Class PassFail Grader Tight Coupling Dependency

S o l u t i o n

class Lecture Class Standard Grader Class PassFail Grader Dependency Abstraction Loose Coupling

S o l u t i o n

class Lecture Class Standard Grader Class PassFail Grader Dependency Abstract Class interface Loose Coupling

S o l u t i o n

class Lecture Dependency Abstract Class interface Loose Coupling

Interface? Discussion

Behavior Discussion

class Lecture grade() Lecture

Grade

Discussion class class class

class Lecture grade() Lecture

Grade

Discussion class class class

class Lecture grade() Lecture

Discussion class class class

class Lecture grade() Lecture

Discussion class class class

class Lecture grade() Lecture

Discussion class class class

class Lecture grade() ,

Lecture

Discussion class class class

class Lecture grade() Lecture

Discussion class class class

Program to an interface, not implementation

class Lecture grade() Java interface Discussion class class class interface

Refactoring

P ro bl e m

class Lecture Class StandardGrader Class PassFailGrader interface Grader Create Dependency Dependency Use Tight Coupling Class Dependency

S o l u t i o n

class Lecture Class StandardGrader Class PassFailGrader interface Grader Create Dependency Dependency Use Separate Use From Construction

S o l u t i o n

class Lecture Class StandardGrader Class PassFailGrader interface Grader Create Dependency Dependency Use Client Dependency Use Separate Use From Construction

S o l u t i o n

class Lecture Class StandardGrader Class PassFailGrader interface Grader Dependency Use Client Dependency Use Separate Use From Construction Create Dependency

S o l u t i o n

class Lecture Class StandardGrader Class PassFailGrader interface Grader Dependency Use Client Dependency Use Separate Use From Construction Create Dependency inject Dependency

Refactoring

Lecture lecture = new Lecture(new StandardGrader(), 80, 90, 65); String grade = lecture.grade(); Lecture lecture = new Lecture(new PassFailGrader(), 80, 90, 65); String grade = lecture.grade(); Lecture Client Lecture (Use) Grader (Create) Lecture (Dependency Injection)

Program to an interface, not implementation Dependency Injection

Lecture lecture = new Lecture(new StandardGrader(), 80, 90, 65); String grade = lecture.grade(); Lecture lecture = new Lecture(new PassFailGrader(), 80, 90, 65); String grade = lecture.grade(); Lecture

?

S o l u t i o n

class Lecture Class StandardGrader Class PassFailGrader interface Grader Dependency Use Client Dependency Use Dependency Injection Framework inject Dependency

Spring

@Controller public class ManageBookController { @Autowired private BookstoreService bookstoreService; @Autowired private CategoryService categoryService;

Dependency Injection & Interface Discussion Flexibility Testability Reusability

Interface & Dynamic Type Language Discussion

class Lecture: def __init__(self, grader, scores): self.scores = scores self.grader = grader def grade(self): return self.grader.grade(self.scores) class StandardGrader: def grade(self): ... class PassFailGrader: def grade(self): ... ex) Python