TDDB84 Design Patterns Lecture 09. State, Prototype, Visitor, Flyweight

Transcription

1 TDDB84 Design Patterns Lecture 09 State, Prototype, Visitor, Flyweight Peter Bunus Department of Computer and Information Science Linköping University, Sweden

2 TDDB84 Design Patterns Slide 2 State

3 TDDB84 Design Patterns Slide 3 State Non Software Example

4 The Gumball Vending Machine Has Quarter Inserts quarter ejects quarter turns crank Out of gumballs No Quarter gumballs=0 gumballs>0 Gumball sold dispense gumballs TDDB84 Design Patterns Slide 4

5 Writting Code public class GumballMachine { final static int SOLD_OUT = 0; final static int NO_QUARTER = 1; final static int HAS_QUARTER = 2; final static int SOLD = 3; Has Quarter Inserts quarter ejects quarter int state = SOLD_OUT; int count = 0; public GumballMachine(int count) { this.count = count; if (count > 0) { state = NO_QUARTER; Out of gumballs No Quarter gumballs=0 turns crank gumballs>0 dispense gumballs Gumball sold TDDB84 Design Patterns Slide 5

6 Writting the Code public void insertquarter() { if (state == HAS_QUARTER) { System.out.println("You can't insert another quarter"); else if (state == NO_QUARTER) { state = HAS_QUARTER; System.out.println("You inserted a quarter"); else if (state == SOLD_OUT) { System.out.println("You can't insert a quarter, the machine is sold out"); else if (state == SOLD) { System.out.println("Please wait, we're already giving you a gumball"); Out of gumballs Has Quarter Inserts quarter ejects quarter turns crank No Quarter gumballs=0 gumballs>0 Gumball sold dispense gumballs TDDB84 Design Patterns Slide 6

7 Writting the Code public void ejectquarter() { if (state == HAS_QUARTER) { System.out.println("Quarter returned"); state = NO_QUARTER; else if (state == NO_QUARTER) { System.out.println("You haven't inserted a quarter"); else if (state == SOLD) { System.out.println("Sorry, you already turned the crank"); else if (state == SOLD_OUT) { System.out.println("You can't eject, Has Quarter you haven't inserted a quarter yet"); Inserts quarter ejects quarter turns crank Out of gumballs No Quarter gumballs=0 gumballs>0 Gumball sold dispense gumballs TDDB84 Design Patterns Slide 7

8 Testing the GumBall Machine public class GumballMachineTestDrive { public static void main(string[] args) { GumballMachine gumballmachine = new GumballMachine(5); System.out.println(gumballMachine); gumballmachine.insertquarter(); gumballmachine.turncrank(); System.out.println(gumballMachine); gumballmachine.insertquarter(); gumballmachine.ejectquarter(); gumballmachine.turncrank(); System.out.println(gumballMachine); gumballmachine.insertquarter(); gumballmachine.insertquarter(); gumballmachine.turncrank(); gumballmachine.insertquarter(); gumballmachine.turncrank(); gumballmachine.insertquarter(); gumballmachine.turncrank(); System.out.println(gumballMachine); TDDB84 Design Patterns Slide 8

9 You expected it. Isn t it? Joe, we need to reward somehow customers that are constantly buying gums from our machines. Let s implement reward system that gives you a free gum if you already purchased 10 gums. TDDB84 Design Patterns Slide 9

10 What we need to do public class GumballMachine { final static int SOLD_OUT = 0; final static int NO_QUARTER = 1; final static int HAS_QUARTER = 2; final static int SOLD = 3; int state = SOLD_OUT; int count = 0; public void insertquarter(){ //insert quarter code here public void ejectquarter(){ //insert quarter code here public void turncrank(){ //insert quarter code here public void dispense(){ //insert quarter code here TDDB84 Design Patterns Slide 10 You have to add a new WINNER state here...but then, you d have to add a new conditional in every single method to handle the WINNER state, that s a lot of code to modify turncrank() will get especially messy, because you d have to add code to check to see whether you ve got a winner and then switch to either the WINNER state or SOLD state

11 Redesigning the Gumball Machine «interface» State +insertquarter() +ejectquarter() +turncrank() +dispense() SoldState SoldOutState NoQuarterState HasQuarterState +insertquarter() +ejectquarter() +turncrank() +dispense() +insertquarter() +ejectquarter() +turncrank() +dispense() +insertquarter() +ejectquarter() +turncrank() +dispense() +insertquarter() +ejectquarter() +turncrank() +dispense() Has Quarter Inserts quarter ejects quarter turns crank Out of gumballs No Quarter gumballs=0 gumballs>0 Gumball sold TDDB84 Design Patterns Slide 11 dispense gumballs

12 NoQuarterState Has Quarter NoQuarterState Go to HasQuarterState Out of gumballs Inserts quarter ejects quarter turns crank No Quarter +insertquarter() +ejectquarter() +turncrank() +dispense() gumballs=0 gumballs>0 Gumball sold Tell the customer: You haven t inserted a quarter dispense gumballs Tell the customer: You turned, but there's no quarter Tell the customer: You need to pay first TDDB84 Design Patterns Slide 12

13 NoQuarterState public class NoQuarterState implements State { GumballMachine gumballmachine; public NoQuarterState(GumballMachine gumballmachine) { this.gumballmachine = gumballmachine; public void insertquarter() { System.out.println("You inserted a quarter"); gumballmachine.setstate(gumballmachine.gethasquarterstate()); public void ejectquarter() { System.out.println("You haven't inserted a quarter"); public void turncrank() { System.out.println("You turned, but there's no quarter"); public void dispense() { System.out.println("You need to pay first"); public String tostring() { return "waiting for quarter"; TDDB84 Design Patterns Slide 13

14 The State Gumball Machine public class GumballMachine { final static int SOLD_OUT = 0; final static int NO_QUARTER = 1; final static int HAS_QUARTER = 2; final static int SOLD = 3; int state = SOLD_OUT; int count = 0; public class GumballMachine { State soldoutstate; State noquarterstate; State hasquarterstate; State soldstate; State state = soldoutstate; int count = 0; TDDB84 Design Patterns Slide 14

15 The State Gumball Machine public class GumballMachine { State soldoutstate; State noquarterstate; State hasquarterstate; State soldstate; State state = soldoutstate; int count = 0; public GumballMachine(int numbergumballs) { soldoutstate = new SoldOutState(this); noquarterstate = new NoQuarterState(this); hasquarterstate = new HasQuarterState(this); soldstate = new SoldState(this); this.count = numbergumballs; if (numbergumballs > 0) { state = noquarterstate; TDDB84 Design Patterns Slide 15 public void insertquarter() { state.insertquarter(); public void ejectquarter() { state.ejectquarter(); public void turncrank() { state.turncrank(); state.dispense(); void setstate(state state) { this.state = state; void releaseball() { System.out.println("A gumball comes rolling out the slot..."); if (count!= 0) { count = count - 1;

16 The State Design Pattern The Context is the class that can have a number of internal states. The State interface defines common interface for all concrete states; the states all implement the same interface, so they are interchangeable Whenever the request() is made on the Context it is delegated to the state to handle TDDB84 Design Patterns Slide 16 Each concrete class provides its own implementation for a request. In this way, when the Context changes state, its behavior changes as well

17 How about my extra gumball? turns crank winner=0 && gumballs>1 Winner dispense 2 gumballs Has Quarter gumballs=0 gumballs>0inserts quarter ejects quarter turns crank Out of gumballs No Quarter gumballs=0 gumballs>0 Gumball sold dispense gumballs TDDB84 Design Patterns Slide 17

18 The Winner State public class WinnerState implements State { GumballMachine gumballmachine; public WinnerState(GumballMachine gumballmachine) { this.gumballmachine = gumballmachine; public void insertquarter() { System.out.println("Please wait, we're already giving you a Gumball"); public void ejectquarter() { System.out.println("Please wait, we're already giving you a Gumball"); public void turncrank() { System.out.println("Turning again doesn't get you another gumball!"); public void dispense() { System.out.println("YOU'RE A WINNER! You get two gumballs for your quarter"); gumballmachine.releaseball(); if (gumballmachine.getcount() == 0) { gumballmachine.setstate(gumballmachine.getsoldoutstate()); else { gumballmachine.releaseball(); if (gumballmachine.getcount() > 0) { gumballmachine.setstate(gumballmachine.getnoquarterstate()); else { System.out.println("Oops, out of gumballs!"); gumballmachine.setstate(gumballmachine.getsoldoutstate()); TDDB84 Design Patterns Slide 18

19 HasQuarterState public class HasQuarterState implements State { Random randomwinner = new Random(System.currentTimeMillis()); GumballMachine gumballmachine; public HasQuarterState(GumballMachine gumballmachine) { this.gumballmachine = gumballmachine; public void insertquarter() { System.out.println("You can't insert another quarter"); public void ejectquarter() { System.out.println("Quarter returned"); gumballmachine.setstate(gumballmachine.getnoquarterstate()); public void turncrank() { System.out.println("You turned..."); int winner = randomwinner.nextint(10); if ((winner == 0) && (gumballmachine.getcount() > 1)) { gumballmachine.setstate(gumballmachine.getwinnerstate()); else { gumballmachine.setstate(gumballmachine.getsoldstate()); public void dispense() { System.out.println("No gumball dispensed"); TDDB84 Design Patterns Slide 19

20 Gumball Machine TestDrive public class GumballMachineTestDrive { public static void main(string[] args) { GumballMachine gumballmachine = new GumballMachine(10); System.out.println(gumballMachine); gumballmachine.insertquarter(); gumballmachine.turncrank(); gumballmachine.insertquarter(); gumballmachine.turncrank(); System.out.println(gumballMachine); gumballmachine.insertquarter(); gumballmachine.turncrank(); gumballmachine.insertquarter(); gumballmachine.turncrank(); System.out.println(gumballMachine);... TDDB84 Design Patterns Slide 20

21 Prototype 21

22 Prototype Non Software Example 22

23 Motivational Example 23

24 The Prototype Pattern Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype 24

25 Motivational Example - Dragons 25

26 The Dragon Classes class DragonPrototype{ protected: string name; public: ; DragonPrototype(){; DragonPrototype(const DragonPrototype& copy); ~DragonPrototype(){; virtual DragonPrototype* clone() const; void setname(string name); string getname() const; class MultipleHeadedDragon : public DragonPrototype{ protected: int numberofheads; public: MultipleHeadedDragon(){; MultipleHeadedDragon(const MultipleHeadedDragon& copy); ~MultipleHeadedDragon(); virtual DragonPrototype* clone() const; void setnumberofheads(int noheads); int getnumberofheads(); ; 26

27 The Dragon Classes DragonPrototype::DragonPrototype(const DragonPrototype& copy){ name = copy.name; void DragonPrototype::setName(string p_name){ name = p_name; DragonPrototype* DragonPrototype::clone() const{ return new DragonPrototype(*this); MultipleHeadedDragon::MultipleHeadedDragon(const MultipleHeadedDragon &copy): DragonPrototype(copy){ numberofheads = copy.numberofheads; DragonPrototype* MultipleHeadedDragon::clone() const{ return new MultipleHeadedDragon(*this); void MultipleHeadedDragon::setNumberOfHeads(int noheads){ numberofheads = noheads; ; 27

28 The Dragon Client cout << "Testing the dragon prototypes" << endl; MultipleHeadedDragon *dragonmh = new MultipleHeadedDragon(); dragonmh->setname("ziggy"); DragonPrototype *anotherdragon = dragonmh->clone(); anotherdragon->setname("zippy"); dragonmh->setnumberofheads(7); 28

29 The Tree Stooges class Stooge { public: virtual void slap_stick() = 0; ; class Larry: public Stooge { public: void slap_stick(){ cout << "Larry: poke eyes\n"; ; class Moe: public Stooge{ public: void slap_stick(){ cout << "Moe: slap head\n"; ; class Curly: public Stooge{ public: void slap_stick(){ cout << "Curly: suffer abuse\n"; ; 29

30 The Tree Stooges int main(void) { vector roles; int choice; while (true) { cout << "Larry(1) Moe(2) Curly(3) Go(0): "; cin >> choice; if (choice == 0) break; else if (choice == 1) roles.push_back(new Larry); else if (choice == 2) roles.push_back(new Moe); else roles.push_back(new Curly); for (int i = 0; i < roles.size(); i++) roles[i]->slap_stick(); for (int i = 0; i < roles.size(); i++) delete roles[i]; Larry(1) Moe(2) Curly(3) Go(0): 2 Larry(1) Moe(2) Curly(3) Go(0): 1 Larry(1) Moe(2) Curly(3) Go(0): 3 Larry(1) Moe(2) Curly(3) Go(0): 0 Moe: slap head Larry: poke eyes Curly: suffer abuse 30

31 The Tree Stooges Prototype Variant class Stooge { public: ; virtual Stooge* clone() = 0; virtual void slap_stick() = 0; class Larry: public Stooge { public: Stooge* clone() {return new Larry; void slap_stick(){ cout << "Larry: poke eyes\n"; ; class Moe: public Stooge{ public: Stooge* clone() { return new Moe(*this); void slap_stick(){ cout << "Moe: slap head\n"; ; class Curly: public Stooge{ public: Stooge* clone() {return new Curly; void slap_stick(){ cout << "Curly: suffer abuse\n"; ; 31

32 The Tree Stooges Prototype Variant class Factory { public: static Stooge* make_stooge( int choice ); private: static Stooge* s_prototypes[4]; ; Stooge* Factory::s_prototypes[] = { 0, new Larry, new Moe, new Curly ; Stooge* Factory::make_stooge( int choice ) { return s_prototypes[choice]->clone(); 32

33 The Tree Stooges Prototype Variant Larry(1) Moe(2) Curly(3) Go(0): 2 Larry(1) Moe(2) Curly(3) Go(0): 1 Larry(1) Moe(2) Curly(3) Go(0): 3 Larry(1) Moe(2) Curly(3) Go(0): 0 int main( void ) { vector roles; int choice; while (true) { cout << "Larry(1) Moe(2) Curly(3) Go(0): "; cin >> choice; if (choice == 0) break; roles.push_back( Factory::make_stooge( choice ) ); for (int i=0; i < roles.size(); ++i) roles[i]->slap_stick(); for (int i=0; i < roles.size(); ++i) delete roles[i]; Moe: slap head Larry: poke eyes Curly: suffer abuse 33

34 Prototype Pattern Interaction Diagram 34

35 Applicability! The prototype pattern is used when a system should be independent of how its products are created, composed, and represented; and when the classes to instantiate are specified at run-time; for example, the dynamic loading to avoid building a class hierarchy of factories that parallels the class hierarchy of products; or when instances of a class can have one of only a few different combinations of state 35

36 Consequences! Isolating concrete product classes from the client.! Dynamically adding and removing products at run-time.! Specifying new objects by varying values.! Specifying new objects by varying structure.! Reducing the need for sub-classing.! Configuring an application with classes dynamically.! Main liability: Clone() needed. 36

37 Visitor 37

38 Visitor Non Software Example 38

39 Visitor Pattern Structure 39

40 Motivational Example! Asssume that we have a binary tree with an integer in each node and each leaf! We want: To print all the numbers Compute their sum using separate methods

41 Java Tree Implementation -n : int Tree Leaf Node 1 abstract class Tree { protected int n; abstract void print(); abstract int sum(); class Node extends Tree { private Tree left, right; void print() { left.print(), System.out.print(n); right.print(); int sum() { return left.sum() + n + right.sum(); class Leaf extends Tree { void print() { System.out.print(n); int sum() { return n; 41

42 Tree Visitor interface TreeVisitor { void visit(node node); void visit(leaf leaf); Each tree class must have an accept method abstract class Tree { protected int n; abstract void accept(treevisitor visitor); class Leaf extends Tree { void accept(treevisitor visitor) { visitor.visit(this); class Node extends Tree { private Tree left, right; void accept(treevisitor visitor) { left.accept(visitor), visitor.visit(this); right.accept(visitor); 42

43 Tree Print Visitor interface TreeVisitor { void visit(node node); void visit(leaf leaf); class PrintVisitor extends TreeVisitor { public void visit(node node) { System.out.print(node.getN()); public void visit(leaf leaf) { // Usually the visit methods differ. System.out.print(leaf.getN()); The Client TreeVisitor visitor = new PrintVisitor(); Tree tree =... tree.accept(visitor); 43

44 The Sum Visitor interface TreeVisitor { void visit(node node); void visit(leaf leaf); class SumVisitor implements TreeVisitor { int sum = 0; public void visit(node node) { sum += node.getn(); public void visit(leaf leaf) { sum += leaf.getn(); The Client TreeVisitor v = new SumVisitor(); Tree tree =... tree.accept(visitor); 44

45 Visitor Benefits/Drawbacks! Allows you to add operations to a Composite structure without changing the structure itself! Adding new operations is relativelly easy! The code for operations performed by the Visitor is centralized! The Composite classes encapsulation is broken when the Visitor is used! Because the traversal function is involved, changes to Composite are more difficult. 45

46 Flyweight 46

47 The FlyWeight Design Pattern! The Flyweight pattern describes how to share objects to allow their use at fine granularities without prohibitive cost.! A flyweight" object has state-dependent (extrinsic) part (stored or computed by client objects) state-independent (intrinsic) part (stored in the Flyweight) 48

48 Flyweight 50

49 Flyweight Example public interface IAlien { string Shape { get; //intrinsic state Color GetColor(int madlevel); //extrinsic state public class LargeAlien : IAlien { private string shape = "Large Shape"; //intrinsic state string IAlien.Shape{ get { return shape; Color IAlien.GetColor(int madlevel) //extrinsic state { if (madlevel == 0) return Color.Green; else if (madlevel == 1) return Color.Red; else return Color.Blue; public class LittleAlien : IAlien { private string shape = "Little Shape"; //intrinsic state string IAlien.Shape{ get { return shape; Color IAlien.GetColor(int madlevel) //extrinsic state { if (madlevel == 0) return Color.Red; else if (madlevel == 1) return Color.Blue; else return Color.Green; 51

50 public class AlienFactory { private Dictionary<int,> list = new Dictionary<int,>(); public void SaveAlien(int index, IAlien alien){ list.add(index, alien); Flyweight Example public IAlien GetAlien(int index){ return list[index]; 52

51 class Program { static void Main(string[] args) { //create Aliens and store in factory AlienFactory factory = new AlienFactory(); factory.savealien(0, new LargeAlien()); factory.savealien(1, new LittleAlien()); //now access the flyweight objects IAlien a = factory.getalien(0); IAlien b = factory.getalien(1); //show intrinsic states, all accessed in memory without calculations Console.WriteLine("Showing intrinsic states..."); Console.WriteLine("Alien of type 0 is " + a.shape); Console.WriteLine("Alien of type 1 is " + b.shape); //show extrinsic states, need calculations Console.WriteLine("Showing extrinsic states..."); Console.WriteLine("Alien of type 0 is " + a.getcolor(0).tostring()); Console.WriteLine("Alien of type 0 is " + a.getcolor(1).tostring()); Console.WriteLine("Alien of type 1 is " + b.getcolor(0).tostring()); Console.WriteLine("Alien of type 1 is " + b.getcolor(1).tostring()); 53

52 The Constitution of Software Architects! Encapsulate what varies! Program through an interface not to an implementation! Favor Composition over Inheritance! Classes should be open for extension but closed for modification! Don t call us, we ll call you! A Class should have only one reason to change! Depend upon abstractions. Do not depend upon concrete classes.! Strive for loosely coupled designs between objects that interact 54! Only talk to your friends

53 Seven Layers of Architecture Enterprise-Architecture Global-Architecture System-Architecture OO Architecture Application-Architecture Subsystem Macro-Architecture Frameworks Micro-Architecture Design-Patterns Objects OO Programming 55

54 Antipatterns Sources 56

55 Congratulations: You have now completed TDDB84 57