diff --git a/src/main/java/com/github/hcsp/polymorphism/Main.java b/src/main/java/com/github/hcsp/polymorphism/Main.java
index fe62227..19fb157 100644
--- a/src/main/java/com/github/hcsp/polymorphism/Main.java
+++ b/src/main/java/com/github/hcsp/polymorphism/Main.java
@@ -6,7 +6,8 @@ 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/Sub.java b/src/main/java/com/github/hcsp/polymorphism/Sub.java
index 5ead475..e4a0abf 100644
--- a/src/main/java/com/github/hcsp/polymorphism/Sub.java
+++ b/src/main/java/com/github/hcsp/polymorphism/Sub.java
@@ -10,4 +10,5 @@ public void print(ParamBase param) {
     public void print(ParamSub param) {
         System.out.println("I am Sub, the param is ParamSub");
     }
+    public void println(){}
 }