CODEWITHSUNDEEP
c++design-patterns
Jad Al-Hamwi
Jad Al-Hamwi

Reputation: 169

Explanation For Factory Method

I'm learning the factory method,when and why to use,but one thing that was a little bit ambiguous is that why are we using the static keyword for the factory method,can somebody clarify. as shown in the code below:

enum VehicleType { 
    VT_TwoWheeler,    VT_ThreeWheeler,    VT_FourWheeler 
}; 

// Library classes 
class Vehicle { 
public: 
    virtual void printVehicle() = 0; 
    static Vehicle* Create(VehicleType type); 
}; 
class TwoWheeler : public Vehicle { 
public: 
    void printVehicle() { 
        cout << "I am two wheeler" << endl; 
    } 
}; 
class ThreeWheeler : public Vehicle { 
public: 
    void printVehicle() { 
        cout << "I am three wheeler" << endl; 
    } 
}; 
class FourWheeler : public Vehicle { 
    public: 
    void printVehicle() { 
        cout << "I am four wheeler" << endl; 
    } 
}; 

// Factory method to create objects of different types. 
// Change is required only in this function to create a new object type 
Vehicle* Vehicle::Create(VehicleType type) { 
    if (type == VT_TwoWheeler) 
        return new TwoWheeler(); 
    else if (type == VT_ThreeWheeler) 
        return new ThreeWheeler(); 
    else if (type == VT_FourWheeler) 
        return new FourWheeler(); 
    else return NULL; 
}

PS: This code can be found on GeeksForGeeks.

Upvotes: 2

Views: 122

Answers (1)

jacob galam
jacob galam

Reputation: 811

Static method is one method for the type of the class. That means you don't need a variable for the class Vehicle if you call Create method. You call this method like that: Vehicle::Create(YOU_TYPE) and not like 'regular' method with a class variable. Also Vehicle have a pure virtual method, that's why you can't have a variable of this class and there so the method is static.

Upvotes: 1

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