设计原则三：合成复用原则

合成复用原则：继承和组合优先使用组合
```cpp
#include <iostream>
using namespace std;
//继承和组合，优先使用组合

//抽象车
class AbstractCar{
public:
    virtual void run() = 0;
};

//大众车
class Dazhong : public AbstractCar{
public:
    virtual void run(){
        cout << "大众启动..." << endl;
    }
};

//拖拉机
class Tuolaji : public AbstractCar{
public:
    virtual void run(){
        cout << "拖拉机启动..." << endl;
    }
};

//针对具体类，不适用继承
#if 0
class Person : public Tuolaji{
public:
    void Doufeng(){
        run()
    }
};

class PersonB : public Dazhong{
public:
    void Doufeng(){
        run();
    }
};
#endif
//使用组合
class Person{
public:
    void setCar(AbstractCar *car){
        this->mCar = car;
    }
    void Doufeng(){
        this->mCar->run();
    }
private:
    AbstractCar *mCar;
};

void test01(){
    Person *p = new Person;
    AbstractCar* car = new Dazhong;
    p->setCar(car);
    p->Doufeng();
    delete car;

car = new Tuolaji;
    p->setCar(car);
    p->Doufeng();
    delete car;
    delete p;
}

int main(void){
    test01();
    return 0;
}
```