Using strategy Design-Pattern

03 Feb 2016

1. Proc

Reduce overlapping programming
Fiexible

2. Using case

When you have to override a method of Super-Class, don’t override the method. Make to Interface (like AttackBehavior)

3. Example Code

Below code show cons when programmer use Inheritance.

class Character
{
protected :
    virtual void attack()
    {
        printf("kick and punch");
    }
}

class Knight : public Character
{
public :
    void attack() override
    {
        printf("swing sword");
    }
}

class Magician : public Character
{
public :
    void attack() override
    {
        printf("fire fire-ball");
    }
}

If Some Characters(Knight, Thief etc..) have same attack() method "kick and punch", you would copy Knight’s attack() method to other Character classes. Copy make overlapped and inflexible codes. And if you have to change “kick and punch” to "kick and kick", you would change all Characters that defined attack() method to “kick and punch”.

To solve this problem, use Strategy Design-Pattern.


class Behavior
{
    virtual void do() = 0;
}

class AttackBehavior : public Behavior
{
    void do() override
    {
        printf("kick and punch");
    }
}

class MagicBehavior : public Behavior
{
    void do() override
    {
        printf("fire fire-ball");
    }
}

class Character
{

protected :
    Behavior*    _behavior
public:
    Character();
    virtual ~Character();

    void attack()
    {
        _behavior->do();
    }
}

class Knight : public Character
{
public :
    Knight()
    {
        _behavior = new AttackBehavior();
    }
}

class Magician : public Character
{
public :
    Magician()
    {
        _behavior = new MagicBehavior();
    }
}

If Some Characters(Knight, Thief etc..) have same attack() method "kick and punch", set '_behavior' to AttackBehavior. If you have to change method "kick and punch" to "kick and kick", just change AttackBehavior interface.