class AbstractObject {};

class ConcreteObjectA : public AbstractObject {};
class ConcreteObjectB : public AbstractObject {};
class ConcreteObjectNULL : public AbstractObject {};
     
class Factory {
public:
     virtual AbstractObject* do_create() = 0;
     AbstractObject* create_object() {
          return      this->do_create();
     }
};

class FactoryA :public Factory{
public:
     virtual AbstractObject* do_create() {
          return new      ConcreteObjectA;
     }     
};

class FactoryB :public Factory{
public:
     virtual AbstractObject* do_create() {
          return new      ConcreteObjectB;
     }     
};

Factory* factory = new FactoryA;
AbstractObject* obj = factory->create_object();      // 获得ConcreteObjectA对象

class AbstractObject {
public:
     virtual void initialize() {}     
};

class Factory {
public:
     virtual AbstractObject* do_create() = 0;
     AbstractObject* create_object() {
          AbstractObject* obj = this->do_create();
          obj->initialize();
          return      obj;
     }
};

class FactoryA :public Factory{
public:
     virtual AbstractObject* do_create() {
          bool isOk = true;
          // isOk = ...any judgement
          if (isOk)  
               return new      ConcreteObjectA;
          return new ConcreteObjectNULL;
     }     
};