Headfirst设计模式的C++实现——状态模式(State)

state.h

1 #ifndef _STATE_H_
 2 #define _STATE_H_
 3 
 4 class GumballMachine;
 5 
 6 class State {
 7 public:
 8     virtual void insert_quarter() = 0;
 9     virtual void eject_quarter() = 0;
10     virtual void turn_crank() = 0;
11     virtual void dispense() = 0;
12     State( GumballMachine &_gumball_machine ) : gumball_machine (_gumball_machine ) {}
13 protected:
14     GumballMachine &gumball_machine;
15 };
16 #endif

gumball_machine.h

说明：这里之所有要把SoldOutState等状态定义在GumballMachine类之中是因为两者之间有相互的依赖，暂时没有想到其他的解决方法。

1 #ifndef _GUMBALL_MACHINE_H_
  2 #define _GUMBALL_MACHINE_H_
  3 #include <iostream>
  4 #include "state.h"
  5 
  6 class GumballMachine {
  7 private:
  8     class SoldOutState : public State {
  9     public:
 10         SoldOutState( GumballMachine &_gumball_machine ) : State(_gumball_machine) {}
 11         void insert_quarter() {
 12             std::cout << "You can't insert a quarter, the machine is sold out" << std::endl;
 13         }
 14         void eject_quarter() {
 15             std::cout << "you can't eject, you haven't inserted a quarter yet" << std::endl;
 16         }
 17         void turn_crank() {
 18             std::cout << "You turned, but there's no gumballs" << std::endl;
 19         }
 20         void dispense() {
 21             std::cout << "No gumball dispensed" << std::endl;
 22         }
 23     };
 24 
 25     class NoQuarterState : public State {
 26     public:
 27         NoQuarterState( GumballMachine &_gumball_machine ): State(_gumball_machine) {}
 28         void insert_quarter() {
 29             std::cout << "You inserted a quarter" << std::endl;
 30             gumball_machine.set_state( gumball_machine.get_has_quarter_state() );
 31         }
 32         void eject_quarter() {
 33             std::cout << "You haven't inserted a quarter" << std::endl;
 34         }
 35         void turn_crank() {
 36             std::cout << "You turned, but there's no quarter" << std::endl;
 37         }
 38         void dispense() {
 39             std::cout << "You need to pay first" << std::endl;
 40         }
 41     };
 42     
 43     class HasQuarterState : public State {
 44     public:
 45         HasQuarterState( GumballMachine & _gumball_machine ) : State(_gumball_machine) {}
 46         void insert_quarter() {
 47             std::cout << "You can't insert another quarter" << std::endl;
 48         }
 49         void eject_quarter() {
 50             std::cout << "Quarter returned" << std::endl;
 51             gumball_machine.set_state( gumball_machine.get_no_quarter_state() );
 52         }
 53         void turn_crank() {
 54             std::cout << "You turned..." << std::endl;
 55             gumball_machine.set_state( gumball_machine.get_sold_state() );
 56         }
 57         void dispense() {
 58             std::cout << "No gumball dispensed" << std::endl;
 59         } 
 60     };
 61     class SoldState : public State {
 62     public:
 63         SoldState( GumballMachine &_gumball_machine ) : State(_gumball_machine) {}
 64         void insert_quarter() {
 65             std::cout << "Please wait, we're already giving you a gumball" << std::endl;
 66         }
 67         void eject_quarter() {
 68             std::cout << "Sorry, you already turned the crank" << std::endl;
 69         }
 70         void turn_crank() {
 71             std::cout << "Turning twice doesn't get you another gumball!" << std::endl;
 72         }
 73         void dispense() {
 74             gumball_machine.release_ball();
 75             if ( 0 == gumball_machine.get_count() ) {
 76                 gumball_machine.set_state( gumball_machine.get_sold_out_state() );
 77             }
 78             else {
 79                 gumball_machine.set_state( gumball_machine.get_no_quarter_state() );
 80             }
 81         }
 82     };
 83 
 84     SoldOutState sold_out_state;
 85     NoQuarterState no_quarter_state;
 86     HasQuarterState has_quarter_state;
 87     SoldState sold_state;
 88     State *state;
 89     unsigned count;
 90 public:
 91     GumballMachine( unsigned _count ) :
 92         count(_count),
 93         sold_out_state( *this ),
 94         no_quarter_state( *this ),
 95         has_quarter_state( *this ),
 96         sold_state( *this ) {
 97             if ( 0 == count ) {
 98                 state = &sold_out_state;
 99             }
100             else {
101                 state = &no_quarter_state;
102             }
103         }
104     void release_ball() {
105         std::cout << "A gumball comes rolling out the slot" << std::endl;
106         count--;
107         if ( 0 == count ) {
108             std::cout << "Oops, out of gumballs!" << std::endl;
109         }
110     }
111     unsigned get_count() { return count; }
112     void insert_quarter() { state->insert_quarter(); }
113     void eject_quarter() { state->eject_quarter(); }
114     void turn_crank() { state->turn_crank(); state->dispense(); }
115     void set_state( State *_state ) { state = _state; }
116     State *get_sold_out_state() { return &sold_out_state; }
117     State *get_no_quarter_state() { return &no_quarter_state; }
118     State *get_has_quarter_state() { return &has_quarter_state; }
119     State *get_sold_state() { return &sold_state; }
120 };
121 #endif

main.cpp

1 #include "gumball_machine.h"
 2 
 3 int main() {
 4     GumballMachine gumball_machine(2);
 5     
 6     gumball_machine.insert_quarter();
 7     gumball_machine.eject_quarter();
 8     gumball_machine.insert_quarter();
 9     gumball_machine.turn_crank();
10     
11     gumball_machine.insert_quarter();
12     gumball_machine.eject_quarter();
13     gumball_machine.insert_quarter();
14     gumball_machine.turn_crank();
15     
16     
17     gumball_machine.insert_quarter();
18     gumball_machine.eject_quarter();
19     gumball_machine.insert_quarter();
20     gumball_machine.turn_crank();
21     return 0;
22 }

原文链接: https://www.cnblogs.com/ren-yu/p/5496157.html

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