從今天開始，把常用的設計模式都簡單的整理一遍，希望每個星期能至少整理2個模式吧，先從簡單的策略模式開始。
概念：它定義了一系列的算法，并將每一個算法封裝起來，而且使它們還可以相互替換。策略模式讓算法的變化不會影響到使用算法的客戶。
策略模式很簡單，實際上就是OO中的多態，舉個例子，某商場要進行促銷，對于普通顧客打88折，對于銀卡客戶在88折基礎上再滿400減160，對于金卡客戶在88折基礎上再滿400減200。
UML圖如下所示：
接口DiscountStrategy代碼如下：
  public interface DiscountStrategy  {
 public double discount(double sum);
 }
public class GeneralDiscountStrategy implements DiscountStrategy {
@Override
  public double discount(double sum) {
return sum * 0.88;
 }
}
類SilverDiscountStrategy類代碼如下：
public class SilverDiscountStrategy implements DiscountStrategy {
@Override
public double discount(double sum) {
sum = sum * 0.88;
int t = (int) sum / 400;
sum = sum - t * 160;
return sum;
}
}
類GoldenDiscountStrategy代碼如下：
public class GoldenDiscountStrategy implements DiscountStrategy {
@Override
public double discount(double sum) {
sum = sum * 0.88;
int t = (int) sum / 400;
sum = sum - t * 200;
return sum;
}
}
類Cashier代碼如下：
public class Cashier {
private DiscountStrategy discountStrategy = new GeneralDiscountStrategy();
public void getDiscountStrategy(CustomerLevel customerLevel) {
switch (customerLevel) {
case GENERAL:
discountStrategy = new GeneralDiscountStrategy();
break;
case SILVER:
discountStrategy = new SilverDiscountStrategy();
break;
case GOLDEN:
discountStrategy = new GeneralDiscountStrategy();
break;
}
}
public double calculate(double price, int num) {
return discountStrategy.discount(price * num);
}
}
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