使用了策略模式对代码进行重构，使业务与打折策略分离。

src/main/java/com/github/hcsp/polymorphism/Discount95Strategy.java

@@ -1,3 +1,8 @@
 package com.github.hcsp.polymorphism;
 
-public class Discount95Strategy {}
+public class Discount95Strategy extends DiscountStrategy{
+    @Override
+    public int discount(int price, User user) {
+        return (int) (price * 0.95);
+    }
+}

src/main/java/com/github/hcsp/polymorphism/NoDiscountStrategy.java

@@ -1,3 +1,8 @@
 package com.github.hcsp.polymorphism;
 
-public class NoDiscountStrategy {}
+public class NoDiscountStrategy extends DiscountStrategy{
+    @Override
+    public int discount(int price, User user) {
+        return price;
+    }
+}

src/main/java/com/github/hcsp/polymorphism/OnlyVipDiscountStrategy.java

@@ -1,3 +1,11 @@
 package com.github.hcsp.polymorphism;
 
-public class OnlyVipDiscountStrategy {}
+public class OnlyVipDiscountStrategy extends DiscountStrategy{
+    public int discount(int price, User user) {
+        if (user.isVip()) {
+            return (int) (price * 0.95);
+        } else {
+            return price;
+        }
+    }
+}

src/main/java/com/github/hcsp/polymorphism/PriceCalculator.java

@@ -7,8 +7,9 @@ public class PriceCalculator {
     // OnlyVipDiscountStrategy 只有VIP打95折，其他人保持原价
     // 重构后的方法签名：
     // public static int calculatePrice(DiscountStrategy strategy, int price, User user)
-    public static int calculatePrice(String discountStrategy, int price, User user) {
-        switch (discountStrategy) {
+    public static int calculate(DiscountStrategy strategy, int price, User user) {
+        return strategy.discount(price, user);
+      /*  switch (discountStrategy) {
             case "NoDiscount":
                 return price;
             case "Discount95":
@@ -23,6 +24,6 @@ public static int calculatePrice(String discountStrategy, int price, User user)
                 }
             default:
                 throw new IllegalStateException("Should not be here!");
-        }
+        }*/
     }
 }