狀態模式:允許一個對象在其內部狀態改變時改變它的行爲。對象看起來似乎修改了它的類。它有兩種使用情況:(1)一個對象的行爲取決於它的狀態, 並且它必須在運行時刻根據狀態改變它的行爲。(2)一個操作中含有龐大的多分支的條件語句,且這些分支依賴於該對象的狀態。本文的例子爲第一種情況,以戰爭爲例,假設一場戰爭需經歷四個階段:前期、中期、後期、結束。當戰爭處於不同的階段,戰爭的行爲是不一樣的,也就說戰爭的行爲取決於所處的階段,而且隨着時間的推進是動態變化的。下面給出相應的UML圖。
實現的代碼比較簡單,給出War類和State類,War類中含State對象(指針形式)。
- class War;
- class State
- {
- public:
- virtual void Prophase() {}
- virtual void Metaphase() {}
- virtual void Anaphase() {}
- virtual void End() {}
- virtual void CurrentState(War *war) {}
- };
- //戰爭
- class War
- {
- private:
- State *m_state; //目前狀態
- int m_days; //戰爭持續時間
- public:
- War(State *state): m_state(state), m_days(0) {}
- ~War() { delete m_state; }
- int GetDays() { return m_days; }
- void SetDays(int days) { m_days = days; }
- void SetState(State *state) { delete m_state; m_state = state; }
- void GetState() { m_state->CurrentState(this); }
- };
- class War;
- class State
- {
- public:
- virtual void Prophase() {}
- virtual void Metaphase() {}
- virtual void Anaphase() {}
- virtual void End() {}
- virtual void CurrentState(War *war) {}
- };
- //戰爭
- class War
- {
- private:
- State *m_state; //目前狀態
- int m_days; //戰爭持續時間
- public:
- War(State *state): m_state(state), m_days(0) {}
- ~War() { delete m_state; }
- int GetDays() { return m_days; }
- void SetDays(int days) { m_days = days; }
- void SetState(State *state) { delete m_state; m_state = state; }
- void GetState() { m_state->CurrentState(this); }
- };
給出具體的狀態類:
- //戰爭結束
- class EndState: public State
- {
- public:
- void End(War *war) //結束階段的具體行爲
- {
- cout<<"戰爭結束"<<endl;
- }
- void CurrentState(War *war) { End(war); }
- };
- //後期
- class AnaphaseState: public State
- {
- public:
- void Anaphase(War *war) //後期的具體行爲
- {
- if(war->GetDays() < 30)
- cout<<"第"<<war->GetDays()<<"天:戰爭後期,雙方拼死一搏"<<endl;
- else
- {
- war->SetState(new EndState());
- war->GetState();
- }
- }
- void CurrentState(War *war) { Anaphase(war); }
- };
- //中期
- class MetaphaseState: public State
- {
- public:
- void Metaphase(War *war) //中期的具體行爲
- {
- if(war->GetDays() < 20)
- cout<<"第"<<war->GetDays()<<"天:戰爭中期,進入相持階段,雙發各有損耗"<<endl;
- else
- {
- war->SetState(new AnaphaseState());
- war->GetState();
- }
- }
- void CurrentState(War *war) { Metaphase(war); }
- };
- //前期
- class ProphaseState: public State
- {
- public:
- void Prophase(War *war) //前期的具體行爲
- {
- if(war->GetDays() < 10)
- cout<<"第"<<war->GetDays()<<"天:戰爭初期,雙方你來我往,互相試探對方"<<endl;
- else
- {
- war->SetState(new MetaphaseState());
- war->GetState();
- }
- }
- void CurrentState(War *war) { Prophase(war); }
- };
- //戰爭結束
- class EndState: public State
- {
- public:
- void End(War *war) //結束階段的具體行爲
- {
- cout<<"戰爭結束"<<endl;
- }
- void CurrentState(War *war) { End(war); }
- };
- //後期
- class AnaphaseState: public State
- {
- public:
- void Anaphase(War *war) //後期的具體行爲
- {
- if(war->GetDays() < 30)
- cout<<"第"<<war->GetDays()<<"天:戰爭後期,雙方拼死一搏"<<endl;
- else
- {
- war->SetState(new EndState());
- war->GetState();
- }
- }
- void CurrentState(War *war) { Anaphase(war); }
- };
- //中期
- class MetaphaseState: public State
- {
- public:
- void Metaphase(War *war) //中期的具體行爲
- {
- if(war->GetDays() < 20)
- cout<<"第"<<war->GetDays()<<"天:戰爭中期,進入相持階段,雙發各有損耗"<<endl;
- else
- {
- war->SetState(new AnaphaseState());
- war->GetState();
- }
- }
- void CurrentState(War *war) { Metaphase(war); }
- };
- //前期
- class ProphaseState: public State
- {
- public:
- void Prophase(War *war) //前期的具體行爲
- {
- if(war->GetDays() < 10)
- cout<<"第"<<war->GetDays()<<"天:戰爭初期,雙方你來我往,互相試探對方"<<endl;
- else
- {
- war->SetState(new MetaphaseState());
- war->GetState();
- }
- }
- void CurrentState(War *war) { Prophase(war); }
- };
- //測試案例
- int main()
- {
- War *war = new War(new ProphaseState());
- for(int i = 1; i < 40;i += 5)
- {
- war->SetDays(i);
- war->GetState();
- }
- delete war;
- return 0;
- }
- //測試案例
- int main()
- {
- War *war = new War(new ProphaseState());
- for(int i = 1; i < 40;i += 5)
- {
- war->SetDays(i);
- war->GetState();
- }
- delete war;
- return 0;
- }