diff --git a/src/main/java/com/github/hcsp/polymorphism/Main.java b/src/main/java/com/github/hcsp/polymorphism/Main.java
index fe62227..bd2cd82 100644
--- a/src/main/java/com/github/hcsp/polymorphism/Main.java
+++ b/src/main/java/com/github/hcsp/polymorphism/Main.java
@@ -6,7 +6,7 @@ public class Main {
     // "I am Sub, the param is ParamSub"
     public static void main(String[] args) {
         Base object = new Sub();
-        ParamBase param = new ParamSub();
+        ParamSub param = new ParamSub();
         object.print(param);
     }
 }
diff --git a/src/main/java/com/github/hcsp/polymorphism/ParamSub.java b/src/main/java/com/github/hcsp/polymorphism/ParamSub.java
index e9845be..6b6d149 100644
--- a/src/main/java/com/github/hcsp/polymorphism/ParamSub.java
+++ b/src/main/java/com/github/hcsp/polymorphism/ParamSub.java
@@ -1,3 +1,5 @@
 package com.github.hcsp.polymorphism;
 
-public class ParamSub extends ParamBase {}
+public class ParamSub extends ParamBase {
+
+}