设计原则四：依赖倒转原则

![](/media/202401/2024-01-22_084719_4897210.20040830422338618.png)
传统的过程式设计倾向于使用高层次的模块依赖于低层次的模块，抽象层依赖于具体的层次。不利于维护，动一发牵全身。

设计模式中，不再像传统的依赖一层依赖一层，而是都依赖抽象层（即，高层业务依赖于抽象类接口，底层业务也依赖于抽象类接口）

![](/media/202401/2024-01-22_084837_6646310.4621663292595055.png)
```cpp
#include <iostream>
using namespace std;

//依赖倒转原则

#if 0
//底层业务
class BankWorker{
public:
    //存款业务
    void saveService(){
        cout << "办理存款业务" << endl;
    }
    void payService(){
        cout << "办理支付业务" << endl;
    }
    void transferService(){
        cout << "办理转账业务" << endl;
    }
};

//中层模块
void doSaveBussiness(BankWorker* worker){
    worker->saveService();
}

void doPayBussiness(BankWorker* worker){
    worker->payService();
}

void doTransferBussiness(BankWorker* worker){
    worker->transferService();
}

//高层业务
void test01(){
    BankWorker* worker = new BankWorker;
    doSaveBussiness(worker); //办理存款业务
    doPayBussiness(worker); //办理支付业务
    doTransferBussiness(worker); //办理转账业务
}
#endif

//银行工作人员
class AbstractWorker{
public:
    virtual void doBussiness() = 0;
};

//专门办理存款业务的工作人员
class SaveBankWorker : public AbstractWorker{
public:
    virtual void doBussiness(){
        cout << "办理存款业务" << endl;
    }
};

//专门办理支付业务的工作人员
class PayBankWorker : public AbstractWorker{
    virtual void doBussiness(){
        cout << "办理支付业务" << endl;
    }
};

//专门办理转账业务的工作人员
class TransferBankWorker : public AbstractWorker{
    virtual void doBussiness(){
        cout << "办理转账业务" << endl;
    }
};

//中层业务
void doNewBussiness(AbstractWorker* worker){
    worker->doBussiness();
}

void test02(){
    AbstractWorker * worker = new TransferBankWorker;
    doNewBussiness(worker);
    delete worker;
    
    worker = new PayBankWorker;
    doNewBussiness(worker);
    delete worker;

worker = new SaveBankWorker;
    doNewBussiness(worker);
    delete worker; 
}
```