Java封裝商場打折策略(Strategy模式)
阿新 • • 發佈：2018-12-30
有了OO的基礎後，開始認真學習設計模式。
首先學習的是Strategy，下面就封裝商場打折策略來分析下策略模式是怎樣一回事。
商場每逢節假日都會對不同的商品採用不同的打折策略，首先賣蘋果的說我的蘋果要打折，好的，我們建立Market和Apple類。
1 /** 2 * 3 * @author LingJian 4 * 5 */ 6 public class Market { 7 8 /** 9 * 只對Apple 10 * @param apple 11 */ 12 public static void normalSell(Apple apple) {13 System.out.println("未打折價錢:" + apple.getPrice() * apple.getWeight()); 14 } 15 /** 16 * 只對Apple 17 * @param apple 18 */ 19 public static void discountSell(Apple apple) { 20 double weight = apple.getWeight(); 21 //打折演算法 22 if(weight < 10) { 23 normalSell(apple);24 }else if(weight >= 10 && weight < 50) { 25 System.out.println("打八八折價錢:" + apple.getPrice() * apple.getWeight() * 0.88 ); 26 }else if(weight >= 50) { 27 System.out.println("打五折價錢:" + apple.getPrice() * apple.getWeight() * 0.5 ); 28 }29 } 30 }
1 /** 2 * 3 * @author LingJian 4 * 5 */ 6 public class Apple { 7 //重量 8 private double weight; 9 //單價 實際開發中 涉及金錢等精確計算都是用BigDecimal 10 private double price; 11 12 public double getWeight() { 13 return weight; 4 } 15 public void setWeight(double weight) { 16 this.weight = weight; 17 } 18 public double getPrice() { 19 return price; 20 } 21 public void setPrice(double price) { 22 this.price = price; 23 } 24 public Apple(double weight, double price) { 25 super(); 26 this.weight = weight; 27 this.price = price; 28 } 29 30 31 32 }
/** * * @author LingJian * */ public class Test { /** * @param args */ public static void main(String[] args) { //只能對蘋果打折 還不能對通用的一類事物打折 而且都是要賣什麼就寫什麼打折演算法 其實每類事物打折演算法又是不一致的 Apple apple = new Apple(10.35, 3.6); Market.normalSell(apple); Market.discountSell(apple); } }
節假日過了兩天後，賣香蕉的一看，蘋果打折促銷後，原先買香蕉的都跑去買蘋果了，不行，香蕉也要打折，不然賣不出去就爛了，OK，這個時候，我們再往Market加一個賣香蕉的打折方法和Banana類，問題很好的解決了….後來，賣梨賣橙子賣橘子的都來了，但是由於每個商品打折的演算法和策略都不一樣，咱們只能先往Market不停的加方法….顯然這不是很好的設計，不停的寫打折方法就說明我們這個打折方法不夠通用，擴充套件性不強，那這個時候怎麼辦呢？對，肯定是想辦法讓咱們的打折方法通用，增強擴充套件性，那麼說到擴充套件我們肯定得想到OO的核心-多型。
這裡，我們建立一個Discountable介面，讓需要打折的商品都實現這個介面，並且在重寫打折方法，這樣對於Market來說，我們就把具體的打折實現方式都交給了具體的物件本身來實現，我們就不用擔心演算法策略不同而不停的增加方法。
/** * * @author LingJian * */ public class Market { /** * 對可打折的一類事物進行打折 * @param apple */ public static void discountSell(Discountable d) { d.discountSell(); } }
public class Apple implements Discountable { //重量 private double weight; //單價 實際開發中 涉及金錢等精確計算都是用BigDecimal private double price; public double getWeight() { return weight; } public void setWeight(double weight) { this.weight = weight; } public double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public Apple(double weight, double price) { super(); this.weight = weight; this.price = price; } @Override public void discountSell() { //打折演算法 if(weight < 10) { System.out.println("Apple未打折價錢:" + weight * price); }else if(weight >= 10 && weight < 50) { System.out.println("Apple打八八折價錢:" + weight * price * 0.88 ); }else if(weight >= 50) { System.out.println("Apple打五折價錢:" + weight * price * 0.5 ); } } }
/** * * @author LingJian * */ public class Banana implements Discountable { //重量 private double weight; //單價 實際開發中 涉及金錢等精確計算都是用BigDecimal private double price; public double getWeight() { return weight; } public void setWeight(double weight) { this.weight = weight; } public double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public Banana(double weight, double price) { super(); this.weight = weight; this.price = price; } @Override public void discountSell() { //打折演算法 if(weight < 5) { System.out.println("Banana未打折價錢:" + weight * price); }else if(weight >= 5 && weight < 10) { System.out.println("Banana打八八折價錢:" + weight * price * 0.88 ); }else if(weight >= 10) { System.out.println("Banana打五折價錢:" + weight * price * 0.5 ); } } }
/** * * @author LingJian * */ public interface Discountable { public void discountSell(); }
/** * * @author LingJian * */ public class Test { /** * @param args */ public static void main(String[] args) { //可對打折一類事物進行打折啦 先是Apple Discountable d = new Apple(10.35, 3.6); // Discountable d = new Banana(10.35, 1.6); Market.discountSell(d); } }
OK，這一次咱們採用的都是固定的按購買量打折，但是打折的策略演算法是有可能變化的，不一定每次節假日都是按購買量打折，所以咱們的打折策略不能寫死了，得能夠靈活的變化，怎麼辦呢？當然，還是多型，我們再建立一個Discountor介面，而具體的打折策略都交給具體的實現類來實現，再在需要打折的商品類中，讓其持有Discountor介面的實現子類，這樣不管每次打折策略怎麼變化，我們只需要讓打折商品持有不同的實現物件即可靈活的應對變化，這就是策略(Strategy)模式。
/** * * @author LingJian * */ public class Apple implements Discountable { //重量 private double weight; //單價 實際開發中 涉及金錢等精確計算都是用BigDecimal private double price; //按購買量打折 // private Discountor d = new AppleWeightDiscountor(); //按購買總價打折 private Discountor d = new ApplePriceDiscountor(); public double getWeight() { return weight; } public void setWeight(double weight) { this.weight = weight; } public double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public Apple(double weight, double price) { super(); this.weight = weight; this.price = price; } @Override public void discountSell() { d.discount(this); } }
/** * * @author LingJian * */ public interface Discountor { public void discount(Discountable d); }
/** * * @author LingJian * */ public class AppleWeightDiscountor implements Discountor { /** * 按購買量打折 */ @Override public void discount(Discountable d) { Apple apple = (Apple)d; if(apple.getWeight() < 10) { System.out.println("Apple未打折價錢:" + apple.getWeight() * apple.getPrice()); }else if(apple.getWeight() >= 10 && apple.getWeight() < 50) { System.out.println("Apple打八八折價錢:" + apple.getWeight() * apple.getPrice() * 0.88 ); }else if(apple.getWeight() >= 50) { System.out.println("Apple打五折價錢:" + apple.getWeight() * apple.getPrice() * 0.5 ); } } }
/** * * @author LingJian * */ public class ApplePriceDiscountor implements Discountor { /** * 購買滿10元立減1角 * 購買滿20元立減1元 * 購買滿30元立減5元 */ @Override public void discount(Discountable d) { Apple apple = (Apple)d; if(apple.getWeight() * apple.getPrice() < 10) { System.out.println("Apple未打折價錢:" + apple.getWeight() * apple.getPrice()); }else if(apple.getWeight() * apple.getPrice() >= 10 && apple.getWeight() * apple.getPrice() < 20) { System.out.println("Apple購買滿10元立減1角:" + (apple.getWeight() * apple.getPrice() - 0.1) ); }else if(apple.getWeight() * apple.getPrice() >= 20 && apple.getWeight() * apple.getPrice() < 30) { System.out.println("Apple購買滿20元立減1元:" + (apple.getWeight() * apple.getPrice() - 1) ); }else if(apple.getWeight() * apple.getPrice() >= 30) { System.out.println("Apple購買滿30元立減5元:" + (apple.getWeight() * apple.getPrice() - 5) ); } } }
Test類無需改變。
簡單的描繪下封裝商場打折策略的設計圖。如下所示：
Market負責給Discountable的商品打折，而具體的可打折的商品的打折的演算法則交給Discountor的實現子類來具體實現。