Flyweight Chain of Responsibility

Transcription

1 Flyweight Chain of Responsibility Ing. Libor Buš PhD. Department of Software Engineering Faculty of Information Technology Czech Technical University in Prague MI-DPO WS 2010/11, Lecture 11 Evropský sociální fond Praha & EU: Investujeme do vaší budoucnosti 2010, Libor Buš

2 Agenda Flyweight Chain of Responsibility Summary of GoF Design Patterns 2

3 Flyweight

4 Flyweight Use sharing to support large number of fine-grained objects efficiently. 4

5 Flyweight - Motivation 5

6 Flyweight - Motivation No sharing Flyweight 6

7 Flyweight - Motivation 7

8 Flyweight - Applicability All shall apply: Application uses large number of objects Storage costs are high because of the sheer quantity of objects Most object state can be made extrinsic Many groups of objects may be replaced by relatively few shared objects once extrinsic state is removed The application does not depend on objects identity 8

9 Flyweight - Structure FlyweightFactory itsflyweightpool Flyweight GetFlyweight( key) Operation( extrinsicstate) if( itsflyweightpool[ key] exists) { return existing flyweight; else { create new flyweight; add it to itsflyweightpool; return the new flyweight; ConcreteFlyweight intrisicstate Operation( extrinsicstate) Unshared ConcreteFlyweight allstate Operation( extrinsicstate) Client 9

10 Flyweight - Participants Flyweight declares an interface through which flyweights can receive and act on extrinsic state ConcreteFlyweight implements the Flyweight interface adds storage for intrinsic state (independent on the contexts) must be sharable 10

11 Flyweight - Participants UnsharedConcreteFlyweight not shared usually parent of ConcreteFlyweight FlyweightFactory creates and manages flyweight objects ensures that flyweights are shared properly Client maintains references to flyweights computes and stores the extrinsic state of flyweights 11

12 Flyweight Example I public interface LineFlyweight { public Color getcolor(); public void draw(point location); public class Line implements LineFlyweight { private Color m_color; public Line( Color c) { m_color = c; public Color getcolor() { return m_color; public void draw( Point location) { //draw line on screen LineFlyweightFactory factory = new LineFlyweightFactory();... LineFlyweight line = factory.getline( Color.RED); LineFlyweight line2 = factory.getline( Color.RED); //can use the lines independently line.draw( new Point(100, 100)); line2.draw( new Point(200, 100)); 12

13 Flyweight Example I public class LineFlyweightFactory { private List<LineFlyweight> m_pool; public LineFlyweightFactory() { m_pool = new ArrayList<LineFlyweight>(); public LineFlyweight getline( Color c) { for( LineFlyweight line: m_pool) { if( line.getcolor().equals(c)) { return line; LineFlyweight line = new Line(c); m_pool.add(line); return line; 13

14 Flyweight Example II public final class FontData { enum FontEffect { BOLD, ITALIC, SUPERSCRIPT, SUBSCRIPT, STRIKETHROUGH private final int m_pointsize; private final String m_fontface; private final Color m_color; private final Set<FontEffect> m_effects; private FontData( int pointsize, String fontface, Color color, EnumSet<FontEffect> effects) { this.m_pointsize = pointsize; this.m_fontface = fontface; this.m_color = color; this.m_effects = Collections.unmodifiableSet( effects); // Getters for the FontData, but no setters 14

15 Flyweight Related Patterns Composite Flyweight can be used to share leaf nodes State Flyweight can be used to share States Strategy Flyweight can be used to share Strategies 15

16 Chain of Responsibility 16

17 Chain of Responsibility Method of passing a request among a chain of objects. 17

18 Chain of Responsibility - Motivation 18

19 Chain of Responsibility - Applicability More than one object may handle a request and the actual handler is not known in advance Issuing a request to one of several objects without specifying the receiver explicitly Set of objects that can handle a request should be specified dynamically 19

20 Chain of Responsibility - Structure Client Handler HandleRequest() itssuccessor Concrete Handler1 HandleRequest() Concrete Handler2 HandleRequest() :Client :ConcreteHandler :ConcreteHandler 20

21 Chain of Responsibility - Participants Handler defines an interface for handling requests (optional) implements the successor link ConcreteHandler handles requests it is responsible for can access its successor if the ConcreteHandler can handle the request, it does so; otherwise it forwards the request to its successor Client initiates the request to a ConcreteHandler object on the chain 21

22 Chain of Responsibility Handling More Requests Separate handler interfaces public interface HelpHandler { public void handlehelp(); public interface PrintHandler { public void handleprint(); public interface FormatHandler { public void handleformat(); public class ConcreteHandler implements HelpHandler, PrintHandler, FormatHandler { private HelpHandler m_helpsuccessor; private PrintHandler m_printsuccessor; private FormatHandler m_formatsuccessor; public ConcreteHandler( HelpHandler helpsuccessor, PrintHandler printsuccessor, FormatHandler formatsuccessor) { m_helpsuccessor = helpsuccessor; m_printsuccessor = printsuccessor; m_formatsuccessor = formatsuccessor; public void handlehelp() { // We handle help ourselves, so help code is here. public void handleprint() { printsuccessor.handleprint(); public void handleformat() { formatsuccessor.handleformat(); 22

23 Chain of Responsibility Handling More Requests Argument describing type of request public interface Handler { public void handlerequest( String request); public class ConcreteHandler implements Handler { private Handler m_successor; public ConcreteHandler( Handler successor) { m_successor = successor; public void handlerequest( String request) { if ( request.equals("help")) { // We handle help ourselves, so help code is here. else m_successor.handle(request); 23

24 Chain of Responsibility - Applications Exception handling try catch throw Win32 hooks SetWindowsHookEx hook type WH_MOUSE, WH_KEYBOARD address of proc CallNextHookEx LRESULT CALLBACK HookProc( int ncode, WPARAM wparam, LPARAM lparam) { // process event... return CallNextHookEx( NULL, ncode, wparam, lparam); 24

25 Chain of Responsibility - Applications Java 1.0 AWT handling GUI events public boolean action( Event event, Object obj) { if( event.target == test_button) dotestbuttonaction(); else if( event.target == exit_button) doexitbuttonaction(); else return super.action( event,obj); replaced in Java 1.1 AWT by Observer Efficiency all events were propagated even the application did not care about them Flexibility forced inheritance from Component class 25

26 Chain of Responsibility - Consequences Benefits Reduced coupling between sender and receiver Flexibility in assigning responsibilities to objects Liabilities Receipt is not guaranteed Performance 26

27 Composite Chain of Responsibility Related Patterns Component s parent acts as its successor 27

28 References Books: GoF Design Patterns Articles Flyweight java.dzone.com Flyweight Wikipedia Follow the Chain of JavaWorld The Chain of Responsibility pattern's pitfalls and JavaWorld 28