策略模式

策略模式

定义一系列相同名称不同实现的算法（策略），通过一个context类使不同算法可以互相替换，而不影响使用算法的程序。

实现

public class Strategy {
    public static void main(String[] args) {
        ActivityContext activityContext = new ActivityContext(new DiscountActivity(0.8));
        System.out.println(activityContext.activity(800));
        ActivityContext activityContext1 = new ActivityContext(new ReturnCashActivity(300,50));
        System.out.println(activityContext1.activity(800));
    }
}

/**
 * 活动接口
 */
interface Activity{
    double activity(double originPrice);
}

/**
 * 打折活动
 */
class DiscountActivity implements Activity{

    private double discount;

    public DiscountActivity(double discount) {
        this.discount = discount;
    }
    public double activity(double originPrice) {
        return originPrice * discount;
    }
}
/**
 * 满减活动
 */
class ReturnCashActivity implements Activity{

    private double totalPrice;
    private double returnPrice;

    public ReturnCashActivity(double totalPrice, double returnPrice) {
        this.totalPrice = totalPrice;
        this.returnPrice = returnPrice;
    }

    public double activity(double originPrice) {
        double allPrice = (int)(originPrice / totalPrice) * returnPrice;
        return originPrice - allPrice;
    }
}

/**
 * 活动上下文
 */
class ActivityContext{
    private Activity activity;

    public ActivityContext(Activity activity) {
        this.activity = activity;
    }

    public double activity(double originPrice){
        return activity.activity(originPrice);
    }
}

优点（大话设计模式）

• 减少各种算法类和使用算法类的耦合
• 算法类（strategy）为上下文类（Context）定义了可供重用的算法或行为，继承有助于析取出这些算法的公共功能
• 简化了单元测试，每个算法都有自己的类，可以通过自己的接口单独测试。