Update 09-Polymorphism.md

fate-stay-night · web-flow · commit b6a67c2c477f · 2019-09-12T16:23:32.000+08:00
修改笔误变量
diff --git a/docs/book/09-Polymorphism.md b/docs/book/09-Polymorphism.md
@@ -585,7 +585,7 @@ public class FieldAccess {
 输出：
 
 ```
-sup.field = 0, super.getField() = 1
+sup.field = 0, sup.getField() = 1
 sub.field = 1, sub.getField() = 1, sub.getSuperField() = 0
 ```
 
