diff --git a/src/class21/Animal.java b/src/class21/Animal.java
new file mode 100644
index 0000000..b821742
--- /dev/null
+++ b/src/class21/Animal.java
@@ -0,0 +1,8 @@
+package class21;
+
+public class Animal {
+
+    public void run(){
+        System.out.println("动物会跑~~~");
+    }
+}
diff --git a/src/class21/Test.java b/src/class21/Test.java
new file mode 100644
index 0000000..facd954
--- /dev/null
+++ b/src/class21/Test.java
@@ -0,0 +1,10 @@
+package class21;
+
+public class Test {
+    public static void main(String[] args) {
+        Animal a1 = new Wolf();
+        Animal a2 = new Tortoise();
+        a1.run();
+        a2.run();
+    }
+}
diff --git a/src/class21/Tortoise.java b/src/class21/Tortoise.java
new file mode 100644
index 0000000..18075c4
--- /dev/null
+++ b/src/class21/Tortoise.java
@@ -0,0 +1,8 @@
+package class21;
+
+public class Tortoise extends Animal{
+    @Override
+    public void run() {
+        System.out.println("🐢跑的贼慢~~");
+    }
+}
diff --git a/src/class21/Wolf.java b/src/class21/Wolf.java
new file mode 100644
index 0000000..241ef01
--- /dev/null
+++ b/src/class21/Wolf.java
@@ -0,0 +1,8 @@
+package class21;
+
+public class Wolf extends Animal{
+    @Override
+    public void run() {
+        System.out.println("狼跑的贼溜~");
+    }
+}