角色在策略中的转变

现在让我们举个例子，创建两个人，因为在交易中所处的角色不同，而执行不同的行为。 

首先，创建产品

public class Product
    ...{
        private String name;
        private String description;
        private double cost;
        
        public Product(String name,String description,double cost)
            ...{
                this.name = name;
                this.description = description;
                this.cost = cost;
            }
        
        public double getCost()
            ...{
                return cost;
            }

        public String getDescription()
            ...{
                return description;
            }

        public void setDescription(String description)
            ...{
                this.description = description;
            }

        public String getName()
            ...{
                return name;
            }

        public void setName(String name)
            ...{
                this.name = name;
            }

        public void setCost(double cost)
            ...{
                this.cost = cost;
            }
    }

 

然后创建一个公共的角色类，他抽象了各个角色在交易中所要达成的共同目的，就是是否对交易满意

public interface Role
    ...{
        public boolean isSatisfied(Product product , double price);
    }

 

接着在抽象的角色上，创建买卖双方的类。
先是卖方，他要达成满意，必须有20%的利润

public class Seller implements Role
    ...{
        public boolean isSatisfied(Product product, double price)
        ...{
            if (price - product.getCost() > product.getCost() * 0.2)
                ...{
                    return true;
                }
            else 
                return false;
        }
    }

再是买方，他要达成满意，不能超过其心理价位，而且不能超过商品价值的2倍

public class Buyer implements Role
    ...{
        private double limit;
        public Buyer(double limit)
            ...{
                this.limit = limit;
            }
        public boolean isSatisfied(Product product, double price)
            ...{
                if (price < limit && price < product.getCost() * 2)
                    ...{
                        return true;
                    }
                else
                    return false;
            }
    }

 

最后让我们来创建交易。交易中有两个人，一个是“Tim”，一个是“Allison”。第一笔交易是一套房子，成本价是40万，Tim是买方，Allison是卖方。第二笔交易是一辆成本为5万的车子，Allison变成了买方。

public class Trade
    ...{
        public static void main(String[] args)
            ...{
                Product house = new Product("house", "House Cost 40WangYuan", 400000);
                Product car = new Product("car", "Car Cost 5WangYuan", 50000);
                Person tim = new Person("Tim");
                Person allison = new Person("Allison");
                
                tim.setRole(new Buyer(500000));
                allison.setRole(new Seller());
                
                if (!allison.satisfied(house, 400000))
                    ...{
                        System.out.println(house.getDescription() + " offer of 400,000 is no good for the seller");
                    }
                if (!tim.satisfied(house, 600000))
                    ...{
                        System.out.println(house.getDescription() + " offer of 600,000 is no good for the buyer");
                    }
                if (tim.satisfied(house, 450000))
                    ...{
                        System.out.println(house.getDescription() + " they both agree with 450000");
                    }
                allison.setRole(new Buyer(70000));
                if (allison.satisfied(car, 60000))
                    ...{
                        System.out.println("As a buyer she can afford the " + car.getDescription());
                    }
            }
    }