装饰图案 |设置 3（编码设计）

我们已经在第 1 组中讨论了 Pizza 设计问题和解决它的不同天真方法。我们还在第 2 组中引入了装饰器模式。

在本文中，讨论了 Pizza 问题的装饰器模式的设计和实现。强烈建议您先自己尝试一下。

新建类图(点击图片看清楚)

• Pizza充当我们的抽象组件类。
• 有四个具体组件，即PeppyPaneer 、 FarmHouse 、 Margherita 、 ChickenFiesta 。
• ToppingsDecorator是我们的抽象装饰器，而FreshTomato 、 Paneer 、 Jalapeno 、 Barbeque是具体装饰器。

下面是上述设计的Java实现。

// Java program to demonstrate Decorator
// pattern
  
// Abstract Pizza class (All classes extend
// from this)
abstract class Pizza
{
    // it is an abstract pizza
    String description = "Unkknown Pizza";
  
    public String getDescription()
    {
        return description;
    }
  
    public abstract int getCost();
}
  
// The decorator class :  It extends Pizza to be
// interchangable with it topings decorator can
// also be implemented as an interface
abstract class ToppingsDecorator extends Pizza
{
    public abstract String getDescription();
}
  
// Concrete pizza classes
class PeppyPaneer extends Pizza
{
    public PeppyPaneer() { description = "PeppyPaneer"; }
    public int getCost() {  return 100; }
}
class FarmHouse extends Pizza
{
    public FarmHouse() {  description = "FarmHouse"; }
    public int getCost() { return 200; }
}
class Margherita extends Pizza
{
    public Margherita()  { description = "Margherita"; }
    public int getCost() { return 100;  }
}
class ChickenFiesta extends Pizza
{
    public ChickenFiesta() { description = "ChickenFiesta";}
    public int getCost() { return 200; }
}
class SimplePizza extends Pizza
{
public SimplePizza() { description = "SimplePizza"; }
public int getCost() {  return 50;  }
}
  
// Concrete toppings classes
class FreshTomato extends ToppingsDecorator
{
    // we need a reference to obj we are decorating
    Pizza pizza;
  
    public FreshTomato(Pizza pizza) { this.pizza = pizza; }
    public String getDescription() {
        return pizza.getDescription() + ", Fresh Tomato ";
    }
    public int getCost() { return 40 + pizza.getCost(); }
}
class Barbeque extends ToppingsDecorator
{
    Pizza pizza;
    public Barbeque(Pizza pizza) {  this.pizza = pizza;  }
    public String getDescription() {
        return pizza.getDescription() + ", Barbeque ";
    }
    public int getCost() { return 90 + pizza.getCost(); }
}
class Paneer extends ToppingsDecorator
{
    Pizza pizza;
    public Paneer(Pizza pizza)  {  this.pizza = pizza; }
    public String getDescription() {
        return pizza.getDescription() + ", Paneer ";
    }
    public int getCost()  {  return 70 + pizza.getCost(); }
}
  
// Other toppings can be coded in a similar way
  
// Driver class and method
class PizzaStore
{
    public static void main(String args[])
    {
        // create new margherita pizza
        Pizza pizza = new Margherita();
        System.out.println( pizza.getDescription() +
                         " Cost :" + pizza.getCost());
  
        // create new FarmHouse pizza
        Pizza pizza2 = new FarmHouse();
  
        // decorate it with freshtomato topping
        pizza2 = new FreshTomato(pizza2);
  
        //decorate it with paneer topping
        pizza2 = new Paneer(pizza2);
  
        System.out.println( pizza2.getDescription() +
                         " Cost :" + pizza2.getCost());
        Pizza pizza3 = new Barbeque(null);    //no specific pizza
        System.out.println( pizza3.getDescription() + "  Cost :" + pizza3.getCost());
   }
}

输出：

Margherita Cost :100
FarmHouse, Fresh Tomato , Paneer Cost :310

请注意我们如何在不改变先前测试的代码的情况下添加/删除新的比萨饼和配料，并且配料和比萨饼是分离的。

// CPP program to demonstrate 
// Decorator pattern
#include 
#include 
using namespace std;
  
// Component 
class MilkShake
{
public:
    virtual string Serve() = 0;
    virtual float price() = 0;
};
  
  
// Concrete Component  
class BaseMilkShake : public MilkShake
{
public:
    string Serve()
    {
        return "MilkShake";
    }
  
    float price()
    {
        return 30;
    }
};
  
// Decorator 
class MilkShakeDecorator: public MilkShake
{
protected:
    MilkShake *m_MilkShake;
public:
  
    MilkShakeDecorator(MilkShake *baseMilkShake): m_MilkShake(baseMilkShake){}
  
    string Serve()
    {
        return m_MilkShake->Serve();
    }
  
    float price()
    {
        return m_MilkShake->price();
    }
};
  
  
// Concrete Decorator 
class MangoMilkShake: public MilkShakeDecorator
{
public:
    MangoMilkShake(MilkShake *baseMilkShake): MilkShakeDecorator(baseMilkShake){}
  
    string Serve()
    {
        return m_MilkShake->Serve() + " decorated with Mango ";
    }
    float price()
    {
        return m_MilkShake->price() + 40;
    }
};
  
  
class VanillaMilkShake: public MilkShakeDecorator
{
public:
    VanillaMilkShake(MilkShake *baseMilkShake): MilkShakeDecorator(baseMilkShake){}
  
    string Serve()
    {
        return m_MilkShake->Serve() + " decorated with Vanilla ";
    }
    float price()
    {
        return m_MilkShake->price() + 80;
    }
};
  
int main()
{
  MilkShake *baseMilkShake = new BaseMilkShake();
  cout << "Basic Milk shake \n";
  cout << baseMilkShake -> Serve() << endl;
  cout << baseMilkShake -> price() << endl;    
  
  MilkShake *decoratedMilkShake = new MangoMilkShake(baseMilkShake);
  cout << "Mango decorated Milk shake \n";
  cout << decoratedMilkShake -> Serve() << endl;
  cout << decoratedMilkShake -> price() << endl;    
      
  delete decoratedMilkShake;
  
  decoratedMilkShake = new VanillaMilkShake(baseMilkShake);
  cout << "Vanilla decorated Milk shake \n";
  cout << decoratedMilkShake -> Serve() << endl;
  cout << decoratedMilkShake -> price() << endl;    
  
 delete decoratedMilkShake;
 delete baseMilkShake;
  return 0;
} 

输出：

Basic Milk shake
MilkShake
Price of MilkShake : 30
Mango decorated Milk shake
MilkShake decorated with Mango
Price of Mango MilkShake : 70
Vanilla decorated Milk shake
MilkShake decorated with Vanilla
Price of Vanilla MilkShake : 110