DOCSLIB.ORG

CS 326 Design Patterns What Is a Design Pattern? Example 1

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

What is a Design Pattern? • A standard solution to a common programming problem CS 326 Design Patterns Stephen Freund Example 1: Encapsulation Example 2: Inheritance • Problem: Exposed properties can be directly • Problem: Repetition in implementations manipulated – Similar abstractions have similar components – Violations of the representation invariant • Solution: Inherit default members from a – Dependences prevent changing the implementation superclass • Solution: Hide some components – Select an implementation via run-time dispatching – Constrain ways to access the object • Disadvantages: • Disadvantages: – Code for a class is spread out, and thus less – Interface may not (efficiently) provide all desired understandable operations to all clients – Hard to design and specify a superclass ahead of time – Indirection may reduce performance – Run-time dispatching introduces overhead 1 Example 3: Iteration Example 4: Generics • Problem: To access all members of a collection, need a • Problem: specialized traversal for each data structure – Well-designed data structures only hold one type of – Introduces undesirable dependences object – Does not generalize to other collections • Solution: • Solution: – Programming language checks for errors in contents – The implementation provides traversal abstraction, does bookkeeping – Set<Int> instead of just Set – Results are communicated to clients via a standard interface • Disadvantages: (eg: Sequence methods) – More verbose types • Disadvantages: – Sometimes less understandable error messages – Iteration order fixed by the implementation and not under the control of the client Other Examples Design Pattern in More Detail • Reuse implementation without subtyping • A standard solution to a common programming • Reuse implementation, but change interface problem • Permit a class to be instantiated only once – A design or implementation structure that achieves a • Constructor that might return an existing object particular purpose • Constructor that might return a subclass object – A high-level programming idiom • Combine behaviors without compile-time • A technique for making code more flexible extends clauses – Reduce coupling among program components • Shorthand for describing software design • You could come up with a solution to all of these – connections among components, heap structure, ... on your own, but why reinvent the wheel??? • Vocabulary for communication and documentation 2 When To Use A Design Pattern Canonical Reference • Rule #1: Delay to avoid over-thinking – Get something basic and concrete working first – Improve or generalize it once you understand it • Design patterns can increase / decrease understandability – Improves modularity and flexibility, separates concerns, eases description – But usually adds indirection, increases code size • If you encounter a design problem, consider • aka: "Gang Of Four" Book design patterns that address that problem Three Kinds Of Patterns Creational Patterns • Creational patterns • Initializers are inflexible – constructing objects – Can't return a subtype of class they belong to • Structural patterns – Create new object, and never re-use existing one – combining objects, controlling heap layout • Behavioral patterns • Factory Patterns – communicating among objects, affecting object – ADT creators that are not Swift init()s semantics • Sharing Patterns: – Reuse objects to save space or share common state 3 Factories: Changing Implementations A Factory • Supertypes support multiple implementations class MatrixFactory { public static func createMatrix() -> Matrix { – protocol Matrix { ... } ... – class SparseMatrix : Matrix { ... } return SparseMatrix() – class DenseMatrix : Matrix { ... } } • Clients use the supertype (Matrix) but still create } objects: • Clients call MatrixFactory.createMatrix() – let m : Matrix = SparseMatrix() or instead of a particular constructor – let m : Matrix = DenseMatrix() or ... +To switch implementation, change only one place • Switching implementations requires changing +createMatrix() can do arbitrary code computations to decide what kind of matrix to make Example: Bicycle race Factory Method for Bicycles class Race { public init() { class Race { let bike1 = Bicycle() func createBicycle() -> Bicycle { let bike2 = Bicycle() Bicycle() … class TourDeFrance : Race { } class TourDeFrance : Race { } public init() { init() { func createBicycle() -> Bicycle { … let bike1 = RoadBicycle() let bike1 = RoadBicycle() } } let bike2 = RoadBicycle() createBicycle() … … class Cyclocross : Race { let bike2 = } } public init() { … createBicycle() let bike1 = MountainBicycle() class Cyclocross : Race { } … let bike2 = MountainBicycle() func createBicycle() -> Bicycle { … } MountainBicycle() … } } … … } } } 4 Factory Object for Bicycles Passing Factory Objects Around class BicycleFactory { func createBicycle() -> Bicycle { ... } class Race { func createWheel() -> Wheel { ... } init(factory : BicycleFactory) { func createFrame() -> Frame { ... } let bike1 = factory.createBicycle() } let bike2 = factory.createBicycle() … class RoadBicycleFactory: BicycleFactory { } override func createBicycle() -> Bicycle { } RoadBicycle() } class TourDeFrance : Race { } init() { super.init(factory: RoadBicycleFactory()) } } class MoutainBicycleFactory: BicycleFactory { class Cyclocross: Race { override func createBicycle() -> Bicycle { init() { super.init(factory: MountainBikFactory()) } MoutainBicycle() } } } Separate Control of Bicycles / Races External Dependency Injection class Race { • Java Example: init(factory : BicycleFactory) { – BicycleFactory f = new UnicycleFactory(); let bike1 = factory.createBicycle() – Race r = new TourDeFrance(f); let bike2 = factory.createBicycle() … • With external dependency injection: } – BicycleFactory f = ((BicycleFactory) } DependencyManager.get("BicycleFactory")); – Race r = new TourDeFrance(f); class TourDeFrance : Race { init(factory : BicycleFactory) { • Plus an external file: super.init(factory: factory) <service-point id="BicycleFactory"> } <invoke-factory> <construct class="Bicycle"> init() { super.init(factory: RoadBicycleFactory()) } <service>Tricycle</service> } </construct> </invoke-factory> + Change the factory without recompiling let race = TourDeFrance(factory: unicycleFactory) </service-point> - External file is essential part of program 5 External Dependency Injection Factories: Summary • Interface Builder and Storyboards... • Problem: Want more flexible abstractions for what class to instantiate. • Factory method – Call method that can do any computation and return any subtype • Factory object – Bundles factory methods for a family of types – Can store factory object, pass to constructors, etc. • Dependency Injection – Put choice of subclass in a file to avoid source-code changes or even recompiling when decision changes Design Patterns for Sharing Singleton • Problem: Swift initializers always return a new • Only one object of the given type exists object, never a pre-existing object • Good for unique, shared resources – UserDefaults.standard – DispatchQueue.main • Singleton: only one object exists at runtime – UIApplication.sharedApplication() – Factory method returns the same object every time – Logger for diagnostic messages • Better than lots of global properties • Interning: only one object with a particular – logically group related values (abstract) value exists at run time – Can use initializer / factory to customize – Factory method returns an existing object, not a new – eg: Internationalization: messages in a particular one language 6 Creating Singletons Interning pattern • In Swift class: • Reuse existing objects instead of creating new ones – public constant property to hold singleton object "Stephen Freund" name – private initializer street: "47 Lab Campus Drive" address town: "Williamstown, MA 01267" class Logger { ... static public let instance = Logger() "Bill Lenhart" private init() { ... } name street: "47 Lab Campus Drive" } address town: "Williamstown, MA 01267" • In client: class Address : Hashable { let street : String – Refer to the single instance of the Singleton class let town : String – Logger.instance.print("button clicked") ... } Interning pattern Simple Interning Mechanism • Reuse existing objects instead of creating new ones • Maintain a collection of all objects "Stephen Freund" • name If an object already appears, return that instead street: "47 Lab Campus Drive" var interned = Set<Address>() address town: "Williamstown, MA 01267" func intern(_ n : Address) -> Address { ... // inserts if not present, returns elem == n in set. "Bill Lenhart" let (_, memberAfterInsert) = interned.insert(n) name return memberAfterInsert address } • Less space • objects can be compared with === instead of == • Create the object, but perhaps discard it and • Sensible only for immutable objects return another when interning. 7 java.lang.Boolean and Interning public class Boolean { private final boolean value; Should have never been // construct a new Boolean value public Boolean(boolean value) { made public this.value = value; } // Singletons for true and false public static Boolean FALSE = new Boolean(false); public static Boolean TRUE = new Boolean(true); // factory method that uses interning public static Boolean valueOf(boolean value) { return value ? TRUE : FALSE; } Boolean b = Boolean.valueOf(true); } vs Boolean b = new Boolean(true); 8.
Recommended publications
  • Dependency Injection with Unity

    Dependency Injection with Unity

    D EPEN DEPENDENCY INJECTION WITH UNITY Over the years software systems have evolutionarily become more and more patterns & practices D ENCY complex. One of the techniques for dealing with this inherent complexity Proven practices for predictable results of software systems is dependency injection – a design pattern that I allows the removal of hard-coded dependencies and makes it possible to Save time and reduce risk on your NJECT assemble a service by changing dependencies easily, whether at run-time software development projects by or compile-time. It promotes code reuse and loosely-coupled design which incorporating patterns & practices, I leads to more easily maintainable and flexible code. Microsoft’s applied engineering ON guidance that includes both production The guide you are holding in your hands is a primer on using dependency quality source code and documentation. W I injection with Unity – a lightweight extensible dependency injection TH DEPENDENCY INJECTION container built by the Microsoft patterns & practices team. It covers The guidance is designed to help U software development teams: various styles of dependency injection and also additional capabilities N I of Unity container, such as object lifetime management, interception, Make critical design and technology TY and registration by convention. It also discusses the advanced topics of selection decisions by highlighting WITH UNITY enhancing Unity with your custom extensions. the appropriate solution architectures, technologies, and Microsoft products The guide contains plenty of trade-off discussions and tips and tricks for for common scenarios managing your application cross-cutting concerns and making the most out of both dependency injection and Unity. These are accompanied by a Understand the most important Dominic Betts real world example that will help you master the techniques.
  • Designpatternsphp Documentation Release 1.0

    Designpatternsphp Documentation Release 1.0

    DesignPatternsPHP Documentation Release 1.0 Dominik Liebler and contributors Jul 18, 2021 Contents 1 Patterns 3 1.1 Creational................................................3 1.1.1 Abstract Factory........................................3 1.1.2 Builder.............................................8 1.1.3 Factory Method......................................... 13 1.1.4 Pool............................................... 18 1.1.5 Prototype............................................ 21 1.1.6 Simple Factory......................................... 24 1.1.7 Singleton............................................ 26 1.1.8 Static Factory.......................................... 28 1.2 Structural................................................. 30 1.2.1 Adapter / Wrapper....................................... 31 1.2.2 Bridge.............................................. 35 1.2.3 Composite............................................ 39 1.2.4 Data Mapper.......................................... 42 1.2.5 Decorator............................................ 46 1.2.6 Dependency Injection...................................... 50 1.2.7 Facade.............................................. 53 1.2.8 Fluent Interface......................................... 56 1.2.9 Flyweight............................................ 59 1.2.10 Proxy.............................................. 62 1.2.11 Registry............................................. 66 1.3 Behavioral................................................ 69 1.3.1 Chain Of Responsibilities...................................
  • Simple Injector Documentation Release 5

    Simple Injector Documentation Release 5

    Simple Injector Documentation Release 5 Simple Injector Contributors Jul 27, 2021 Contents 1 Quick Start 3 1.1 Overview.................................................3 1.2 Getting started..............................................3 1.3 A Quick Example............................................4 1.3.1 Dependency Injection......................................4 1.3.2 Introducing Simple Injector...................................5 1.4 More information.............................................6 2 Using Simple Injector 7 2.1 Resolving instances...........................................9 2.2 Configuring Simple Injector....................................... 10 2.2.1 Auto-Registration/Batch-registration.............................. 13 2.3 Collections................................................ 14 2.3.1 Collection types......................................... 16 2.3.2 Auto-registering collections.................................. 16 2.3.3 Adding registrations to an existing collection......................... 17 2.4 Verifying the container’s configuration................................. 17 2.5 Automatic constructor injection / auto-wiring.............................. 18 2.6 More information............................................. 19 3 Object Lifetime Management 21 3.1 Transient Lifestyle............................................ 22 3.2 Singleton Lifestyle............................................ 22 3.3 Scoped Lifestyle............................................. 23 3.3.1 Disposing a Scope......................................
  • 1. Difference Between Factory Pattern and Abstract Factory Pattern S.No

    1. Difference Between Factory Pattern and Abstract Factory Pattern S.No

    1. Difference between Factory Pattern and Abstract Factory Pattern S.No Factory Pattern Abstract Factory Pattern 1 Create object through inheritance Create object through composition 2 Produce only one product Produce families of products 3 Implements code in the abstract creator Concrete factories implements factory that make use of the concrete type that method to create product sub class produces 2.Difference between Abstract Factory Pattern And Builder Pattern S.No Builder Pattern Abstract Factory Pattern 1 In Builder Pattern, there will be one Abstract Factory Pattern will return the Director class which will instruct Builder instance directly. class to build the different parts/properties of our object and finally retrieve the object. 2 It will have reference to the created It does not keep the track of it's created object. object. 3.Difference between Builder Pattern And Composite Pattern S.No Builder Pattern Composite Pattern 1 It is used to create group of objects of It creates Parent - Child relations between predefined types. our objects. 4.Difference between MVC and MVP S.No MVP MVC 1 MVP is a bit more complex to MVC is easier to implement than MVP. implement than MVC .Also, it has additional layer for view interfaces. 2 The request is always received by the The request is received by the controller View and delegated to the presenter which in turn gets the required data and which in turn gets the data does the loads up the appropriate view processing 3 The presentation and view logic an be The controller logic can be unit tested.
  • Scala-Language.Pdf

    Scala-Language.Pdf

    Scala Language #scala Table of Contents About 1 Chapter 1: Getting started with Scala Language 2 Remarks 2 Versions 2 Examples 3 Hello World by Defining a 'main' Method 3 Hello World by extending App 4 Delayed Initialization 4 Delayed Initialization 4 Hello World as a script 5 Using the Scala REPL 5 Scala Quicksheet 6 Chapter 2: Annotations 8 Syntax 8 Parameters 8 Remarks 8 Examples 8 Using an Annotation 8 Annotating the main constructor 8 Creating Your Own Annotations 9 Chapter 3: Best Practices 11 Remarks 11 Examples 11 Keep it simple 11 Don't pack too much in one expression. 11 Prefer a Functional Style, Reasonably 12 Chapter 4: Case Classes 13 Syntax 13 Examples 13 Case Class Equality 13 Generated Code Artifacts 13 Case Class Basics 15 Case Classes and Immutabilty 15 Create a Copy of an Object with Certain Changes 16 Single Element Case Classes for Type Safety 16 Chapter 5: Classes and Objects 18 Syntax 18 Examples 18 Instantiate Class Instances 18 Instantiating class with no parameter: {} vs () 19 Singleton & Companion Objects 20 Singleton Objects 20 Companion Objects 20 Objects 21 Instance type checking 21 Constructors 23 Primary Constructor 23 Auxiliary Constructors 24 Chapter 6: Collections 25 Examples 25 Sort A List 25 Create a List containing n copies of x 26 List and Vector Cheatsheet 26 Map Collection Cheatsheet 27 Map and Filter Over A Collection 28 Map 28 Multiplying integer numbers by two 28 Filter 28 Checking pair numbers 28 More Map and Filter examples 29 Introduction to Scala Collections 29 Traversable types 30 Fold 31 Foreach 32 Reduce 32 Chapter 7: Continuations Library 34 Introduction 34 Syntax 34 Remarks 34 Examples 34 Callbacks are Continutations 34 Creating Functions That Take Continuations 35 Chapter 8: Currying 37 Syntax 37 Examples 37 A configurable multiplier as a curried function 37 Multiple parameter groups of different types, currying parameters of arbitrary positions 37 Currying a function with a single parameter group 37 Currying 38 Currying 38 When to use Currying 39 A real world use of Currying.
  • Design Patterns and Software Engineering Techniques for Java, and How They May Apply to Chisel

    Design Patterns and Software Engineering Techniques for Java, and How They May Apply to Chisel

    HOW IT IS DONE IN JAVA Design Patterns and Software Engineering Techniques for Java, and how they may apply to Chisel CS 294-88: Declarative Hardware Design Martin Maas, 03/05/2013 Introduction I Java has been very popular language in production use for a long time (especially enterprise applications). I Significant performance overheads (GC, JIT,...), yet people are using it for big, mission-critical applications. I Reason (arguably): Enforces rigorous design methodology; availability of a large set of design patterns and tools. I Many of these should be applicable to Chisel (Scala is fundamentally similar to Java, concepts may carry over). I Much of this will be familiar to you already - this talk is intended to organize the content and create a basis for discussion of how to use these techniques in Chisel. Talk Organization 1. Design Strategies 2. Dependency Injection 3. Testing & Mocking 4. Java Tools Part I: Design Strategies Strategy 1: Use Interfaces whenever feasibly possible I Na¨ıveStrategy: When using a component, refer to it by its class type and create an instance of that class. Foo foo = new Foo(); I Problem #1: What if we suddenly need to use a different implementation (e.g. for testing)? I Aside: Could use inheritance, but this breaks abstraction - ideally, declare all classes that are not specifically designed to be inherited from as final. I Problem #2: What if we have a class that wants to provide multiple functionalities? I For example: Consider some class SignalToImageDSP representing a pipeline stage that takes signal data and produces image data. Strategy 1: Use Interfaces whenever feasibly possible I Use when initializing a pipeline: SignalDSP prevStage= new SignalDSP(); SignalToImageDSP stage= new SignalToImageDSP(prevStage); ImageDSP nextStage= new ImageProc(stage); I Say we decide at some point that we want to use a truncated version of the pipeline, where the image data is approximated without using sensors.
  • Abstract Factory Pattern Real World Example

    Abstract Factory Pattern Real World Example

    Abstract Factory Pattern Real World Example Sparry Reuven blackmails some spiritual and outact his swimming so fumblingly! Gasper remains unilateral: she embow her observatories allegorize too ninefold? Whining Dirk wince some menstruation and traps his Alain-Fournier so banteringly! Can You Improve This Article? Abstract factory code and features, when there are different flavors of elements of each service and every shape based on objects will implement modular gui design pattern real object step is. Do this pattern is hard before uploading a level, we are prototypical instance creation logic on desktop or dependent products are design pattern is often. Living in real world design pattern real factory world example, real world has a generic interfaces that will post helpful example, amazon web api like services. If i like this Decorator design pattern tutorial in Java then my share remains your friends and colleagues. Let's you factory method with own factory voil here read the. So basically, we release another attribute of abstraction which will identify the location and internally use again car factory implementation without even giving a single hint you the user. Sometimes, it think of patterns as recipes. It is not related to that. This is the Elven Army! In their state, we have been made up of objects of objects. What medium the intent of the merit Pool pattern? Given a real object as needed. This differs from the Observer pattern determined it allows any subscriber implementing an advance event handler to register what and vague topic notifications broadcast radio the publisher. And think is real world you have new instance property from a partial classes one place here abstract container, we have no review stack exchange is not.
  • Injecting Objects in Sealed Code

    Injecting Objects in Sealed Code

    1 Injecting objects in sealed code Dependency Injection With examples in Java Dhanji R. Prasanna MEAP Release: February 2008 Softbound print: August 2009 | 352 pages ISBN: 193398855X This article is excerpted from the upcoming title Dependency Injection by Dhanji R. Prasanna and published by Manning Publications. It shows you how to use inject-sealed, third-party code. For the table of contents, the Author Forum, and other resources, go to http://manning.com/prasanna/. Not all the code you work with is under your control. Many third party libraries come in binary form and cannot be altered to work with dependency injectors. Adding annotations, refactoring with providers or builders, is out of the question. We'll call this sealed code. (Don't confuse this with the C# keyword.) So if we have no control over sealed code, what can be done to make it work with dependency injection? One answer might be to find a way not to use annotations. Injecting with externalized metadata Recall some of the early Spring XML configuration. It eliminates the need for annotations, right off the bat. In essence, moving configuration metadata from source code to an external location (the XML file). Listing 1 shows a sealed class injected purely with externalized metadata. Listing 1: A sealed class injected via external configuration public class Sealed { private final Dependency dep; public Sealed(Dependency dep) { this.dep = dep; } } <!-- XML injector configuration --> <beans> <bean id="sealed" class="Sealed"> <constructor-arg><bean class="Dependency"></constructor-arg> </bean> </beans> Author’s Template Manning Publications Co. 1 2 Here Sealed did not have to change, and the injector configuration is straightforward.
  • Table of Contents

    Table of Contents

    Acknowledgements .................................................................................................................. xiv 1. Introduction ........................................................................................................................... 1 1.1. Why test? .................................................................................................................... 1 1.2. Why should I change my code? ................................................................................... 2 1.3. What is this book not about? ....................................................................................... 3 1.4. How the book is structured .......................................................................................... 4 1.5. Coding conventions ..................................................................................................... 4 1.6. Example code ............................................................................................................. 6 2. Building blocks ...................................................................................................................... 8 2.1. What is an automated test suite? .................................................................................. 8 2.2. Testing frameworks ..................................................................................................... 9 2.3. Hello, world! ..............................................................................................................
  • Injection Pattern for Inserting Privacy Patterns and Services in Software

    Injection Pattern for Inserting Privacy Patterns and Services in Software

    PIP: A (Privacy) Injection Pattern for Inserting Privacy Patterns and Services in Software by Naureen Ali Submitted in partial fulfilment of the requirements for the degree of Master of Computer Science at Dalhousie University Halifax, Nova Scotia November 2015 © Copyright by Naureen Ali, 2015 Table of Contents List of Tables ................................................................................................................................. v List of Figures ............................................................................................................................... vi Abstract ......................................................................................................................................... ix List of Abbreviations Used ........................................................................................................... x Acknowledgement ........................................................................................................................ xi Chapter 1 : Introduction .............................................................................................................. 1 1.1 Research Problem ........................................................................................................ 2 1.2 Research Objectives ..................................................................................................... 3 1.3 Outline .........................................................................................................................
  • Dependency Injection & Design Principles Recap Reid Holmes SOLID (Dependency Inversion)

    Dependency Injection & Design Principles Recap Reid Holmes SOLID (Dependency Inversion)

    Material and some slide content from: - Krzysztof Czarnecki - Ian Sommerville - Head First Design Patterns Dependency Injection & Design Principles Recap Reid Holmes SOLID (Dependency Inversion) ‣ Program to interfaces not to implementations. REID HOLMES - SE2: SOFTWARE DESIGN & ARCHITECTURE (also called inversion of control) Dependency Inversion ‣ Common problem: ‘how can we wire these interfaces together without creating a dependency on their concrete implementations?’ ‣ This often challenges the ‘program to interfaces, not implementations ’ design principle ‣ Would like to reduce (eliminate) coupling between concrete classes ‣ Would like to be able to substitute different implementations without recompiling ‣ e.g., be able to test and deploy the same binary even though some objects may vary ‣ Solution: separate objects from their assemblers REID HOLMES - SE2: SOFTWARE DESIGN & ARCHITECTURE Example Overview Simple Pizza BillingService API public interface IBillingService { /** * Attempts to charge the order to the credit card. Both successful and * failed transactions will be recorded. * * @return a receipt of the transaction. If the charge was successful, the * receipt will be successful. Otherwise, the receipt will contain a * decline note describing why the charge failed. */ Receipt chargeOrder(PizzaOrder order, CreditCard creditCard); } [ Example from: https://code.google.com/p/google-guice/wiki/Motivation ] REID HOLMES - SE2: SOFTWARE DESIGN & ARCHITECTURE Example Overview Charging orders requires a CCProcessor and a TransactionLog
  • Master Thesis

    Master Thesis

    Marea A Tool for Breaking Dependency Cycles Between Packages Master Thesis Bledar Aga Philosophisch-naturwissenschaftlichen Fakultat¨ der Universitat¨ Bern 27. Januar 2015 Prof. Dr. Oscar Nierstrasz MSc. Andrea Caracciolo Software Composition Group Institut fur¨ Informatik und angewandte Mathematik University of Bern, Switzerland Abstract Placing classes, methods, dependencies in wrong packages may generate architectural problems such as dependency cycles. Developers, maintainers and testers very often have to deal with dependency cycles that compromise the modularity of their systems, prevent proper reuse, increase the cost of maintenance and increase the cost of tests. We argue that reengineers do not have adequate tools that support removing the dependencies forming cycles at the package level. We propose Marea, a tool that helps reengineers maintain their object- oriented systems without cyclic dependencies between packages. In our approach, we analyse object-oriented systems by detecting and suggesting to the user which refactoring operations should be used to remove undesirable dependencies. Marea suggests the best sequence of refactoring operations based on the results of a model-based simulation. Moreover, the best path is identified by applying a customised profit function adapted to the user’s needs. Our approach has been validated on real-world Java open source systems. Keywords: Dependency cycles, package cycles, refactoring simulation, software analysis, software quality. 1 Contents 1 Introduction4 1.1 Solution in a Nutshell...........................5 1.2 Benefits..................................5 1.3 Outline..................................6 2 Cyclic Dependencies7 2.1 Terminology................................7 2.2 Types of dependencies..........................8 2.3 Dependency Cycles at the Package Level................ 11 2.4 The Origin of Dependency Cycles...................