Factory Method. Factory Method. Resource Mgt in App Framework. An Example: A Framework for Productivity ( Office ) Applications

Transcription

1 Factory Method Factory Method A method to instantiate a class and initializes a class instance without using its constructors Uses a regular (i.e., non-constructor) method. Lets a class defer instantiation to subclasses. Define an abstract class for creating an instance. Let its subclasses decide which class to instantiate. 1 2 An Example: A for Productivity ( Office ) s framework A set of foundation APIs to implement and run a series of applications. Implement the standard/common functionalities (structures and behaviors) among individual applications Make them reusable/available for individual apps. Make app development easier and faster. s for productivity ( office ) applications e.g.,.net, Microsoft Foundation Class (MFC), Cocoa, OpenOffice, GNOME, KDE, etc. Spreadsheet Presentation App 3 in App management Creating, opening and closing resources such as documents, spreadsheets, presentation sheets, s and notes. Saving resources in the local disk or a remote cloud. Renaming resources. Exporting resources as other formats. Here, we focus on the creation of resources. Spreadsheet Presentation In/Out App 4

2 In Microsoft Office s Assumptions for Creation Multiple applications exist on an app framework. Extra applications may be developed in the near future. Different applications create and use different types of resources. When an application creates a new resource, it opens a blank resource. Each application creates one resource at a time, but can keep multiple resources open. Each application records the list of resources that it opened recently. 5 6 Requirements for Creation Multiple applications exist. Different applications create and use different types of resources. When an application creates a new resource, it opens a blank resource. should create a document. Excel should create a spreadsheet. PPT should create a slide set. Excel PPT Doc Spreadsheet SlideSet Excel PPT Doc Spreadsheet SlideSet Spreadsheet Presentation Spreadsheet Presentation App 7 App 8

3 Each application creates one resource at a time, but can keep multiple resources open. Each application records the list of resources that it opened recently. Extra applications may be developed in the near future. An app to be developed in the future should create a particular resource associated to that app. We don t know the app-resource pair now. How can we implement the common creation logic in the framework level (i.e., with and ) without knowing s and s subclasses? Excel PPT Doc Spreadsheet SlideSet Excel PPT Doc Spreadsheet SlideSet Spreadsheet Presentation Spreadsheet Presentation App 9 App 10 Solve this Design Issue with Factory Method + new(): # create(): + getopens(): ArrayList<> + getrecents(): ArrayList<> protected and abstract - opens - recents Create a resource, open it, and add it to opens and recents. + new(): # create(): + getopens(): ArrayList<> + getrecents(): ArrayList<> - opens - recents Create a resource, open it, and add it to opens and recents. # create(): Create an instance of Doc and return it. Doc 11 word = new (); word.new(); 12

4 + new(): # create(): + getopens(): ArrayList<> + getrecents(): ArrayList<> # create(): word = new (); word.new(); - opens - recents res = create(); res.open(); opens.put(res); recents.put(res); return res; return new Doc(); Doc 13 The framework What s the Point? new() provides a skeleton (or template) for resource creation. Partially implements a common procedural sequence for resource creation. Never specify specific types (specific class names) for apps and their resources. (framework client) Reuses the skeleton/template for resource creation and completes it By specifying which application class and which resource class are used. 14 What Factory Method Does Define a factory method (new()) in. Have it implement a common procedural sequence (a skeleton or template) for resource creation and initialization with an empty protected method (create()). Benefits The framework Can define a common procedural sequence (a skeleton or template) for resource creation and initialization. Allows individual apps to reuse it. Less redundant code in apps. Does not have to know app-resource pairs (i.e., which specific apps uses which specific resources). 15 Can force every single app to follow the same behavior (i.e. same sequence for instance creation and initialization) when it creates a new resource. 16

5 Another Example: in Integrated Development Environments (IDEs) Imagine an IDE like Eclipse, for example. s in an IDE Programs (e.g., Java, JavaScript, C++, etc.) XML files (e.g., build.xml for Ant, web.xml for Servlet WAR), etc. s, Syntax Highlighters and s IDE Many IDE components (e.g., plugins) use resources. s, syntax highlighters, etc. Java Java XML XML C++ C++ Java JSP Ant C++ LaTeX XMLHighlighter C++Highlighter Syntax highlighting Eclipse 17 Java XML C++ 18 Java XML C++ Java XML C++ How does an editor create a resource? How does it create a syntax highlighter for the resource? Java XML C++ 19 Java XML C++ 20

6 If We don t Factory Method This IDE Is not that developer friendly. Requires developers to write redundant code for their editors (e.g., Java). Java +Java() XML C++ +C++() +XML() Create a Java file, open it, and add it to opens and recents, and set a syntax checker for Java. Create a XML file, open it, and add it to opens and recents, and set a syntax checker for XML. Create a C++ file, open it, and add it to opens and recents, and set a syntax checker for C++. Java XML C++ 21 Can be more developer friendly By defining a common sequence (or skeleton/template) to create and initialize a resource in. Does not have to require developers to write redundant code. 22 Java XML C++ Dilemma How can we implement a common sequence (skeleton or template) for instance creation and initialization in WITHOUT knowing specific subclasses of, and AND relationships among them? What to Do with Factory Method Define a factory method in. Have it implement a common sequence (skeleton or template) for instance creation and initialization with empty protected methods. Java Java JavaHighligher XML XML XMLHighlighter Java XML C

7 res = create(); setsyntaxhighligher(); res.open(); opens.put(res); recents.put(res); return res; -opens + new(): # create(): # set(): void + getopens(): ArrayList<> + getrecents(): ArrayList<> + getsyntaxchecker(): SyntaxChecker -recents Java Benefits This IDE Can define a common sequence (a skeleton or template) for instance creation and initialization Allows individual editors to reuse it. Less redundant code Java + Java() # create(): # setsyntaxhighlughter(): void editor = new Java(); editor.new(); 0..1 return new Java(); -syntaxhighlighter syntaxhighlighter = new JavaChecker(); +check() 25 Does not have to know editor-resource-syntax highlighter mappings. Can force every single editor to follow the same behavior (i.e. same sequence for instance creation and initialization) when it creates a new resource. 26 One More Example: Web App Dev Assume you are implementing a development framework for various web apps. s for web applications e.g., WebKit, Struts, Ruby on Rails, etc. WebKit ( Web browsers (incl. Safari), Dashboard, Mail and many other Mac OS X apps. Assume you are implementing an object pooling API in this framework. Creates and manages a pool of (the same kind/type of) objects e.g., a pool of browser windows, a pool of tabs in each browser window, a pool (cache) of HTML files, a pool of HTTP connections, a pool of threads, etc. Here, we focus on the creation of pools. Safari Dashboard Mail Safari Dashboard Mail Object ing HTML Rendering HTTP Conn Handling WebApp 27 WebApp 28

8 Background: Web Page Caching A web server Receives a connection establishment request from a client (browser). Receives an HTTP command Retrieves a target HTML file from the local disk and returns it to the client. May cache a set of HTML files that have been accessed in the past. Keep them in the memory Faster response to the clients Memory access is much faster than disk access. Factory Method in Object ing + create(numelements: int) registerelement(idcounter, e); Element 30 HTML File Caching + create(numelements: int) registerelement(idcounter, e); Element + create(numelements: int) MyApp registerelement(idcounter, e); Element return new HTMLFile(); MyApp FileCache - cachetable: Hashmap<int, HTMLFile> # registerelement(id:int, e: Element) return new HTMLFile(); -cachetable cachetable.put(id, (HTMLFile)e); HTMLFile FileCache - pooltable: Hashmap<int, HTMLFile> # registerelement(id:int, e: Element) FileCache cache = new FileCache(); cache.create(10); -cachetable cachetable.put(id, (HTMLFile)e); HTMLFile 31 32

9 Factory Method createelement() Allows create() to avoid stating the class name for pool elements. Allows the framework to be independent (or de-coupled) from individual applications (framework clients). Allows applications to be pluggable to the framework. One Step Further create(numelements); +(numelements: int) - create(numelements: int) registerelement(idcounter, e); Element + create(numelements: int) registerelement(idcounter, e); Element 33 MyApp FileCache - pooltable: Hashmap<int, HTMLFile> +FileCache(numElements: int) # registerelement(id:int, e: Element) pooltable.put(id, (HTMLFile)e); super(numelements); return new HTMLFile(); pooltable HTMLFile Client code gets simpler: FileCache cache = new FileCache(10); 34 Client code can be simpler in this alternative design FileCache cache = new FileCache(10); No need to call create() as in the previous design. 35