diff --git a/day10/src/com/inmind/duotai08/downcast/Animal.java b/day10/src/com/inmind/duotai08/downcast/Animal.java
new file mode 100644
index 0000000..9eb1bc8
--- /dev/null
+++ b/day10/src/com/inmind/duotai08/downcast/Animal.java
@@ -0,0 +1,9 @@
+package com.inmind.duotai08.downcast;
+
+public abstract class Animal {
+    String name;
+    int age;
+
+    //吃的行为
+    public abstract void eat();
+}
diff --git a/day10/src/com/inmind/duotai08/downcast/Cat.java b/day10/src/com/inmind/duotai08/downcast/Cat.java
new file mode 100644
index 0000000..1f4d8c6
--- /dev/null
+++ b/day10/src/com/inmind/duotai08/downcast/Cat.java
@@ -0,0 +1,12 @@
+package com.inmind.duotai08.downcast;
+
+public class Cat extends Animal{
+    @Override
+    public void eat() {
+        System.out.println("猫吃鱼");
+    }
+
+    public void catchMouse(){
+        System.out.println("猫抓老鼠");
+    }
+}
diff --git a/day10/src/com/inmind/duotai08/downcast/Demo10.java b/day10/src/com/inmind/duotai08/downcast/Demo10.java
new file mode 100644
index 0000000..abe8748
--- /dev/null
+++ b/day10/src/com/inmind/duotai08/downcast/Demo10.java
@@ -0,0 +1,23 @@
+package com.inmind.duotai08.downcast;
+/*
+学习的对象的向上转型和向下转型，也就是引用数据类型的数据类型转换（自动转换和强制类型转换）
+
+注意：多态的向下转型时，一定要是对应的类型才能转换，否则会报错java.lang.ClassCastException（类型转换异常）
+ */
+public class Demo10 {
+    public static void main(String[] args) {
+        //多态的写法
+        Animal a = new Dog();//父类引用指向子类对象，对象的向上转型，非常安全
+        a.eat();
+        //a.watchDoor();//编译看左边
+
+        //现在a就是一只狗，我想让它看门
+        Dog dog = (Dog) a;
+        dog.watchDoor();
+
+        //现在a是一个动物，让它变成猫，抓老鼠
+        Cat cat = (Cat) a;
+        cat.catchMouse();
+
+    }
+}
diff --git a/day10/src/com/inmind/duotai08/downcast/Dog.java b/day10/src/com/inmind/duotai08/downcast/Dog.java
new file mode 100644
index 0000000..4116617
--- /dev/null
+++ b/day10/src/com/inmind/duotai08/downcast/Dog.java
@@ -0,0 +1,12 @@
+package com.inmind.duotai08.downcast;
+
+public class Dog extends Animal{
+    @Override
+    public void eat() {
+        System.out.println("狗吃骨头");
+    }
+
+    public void watchDoor(){
+        System.out.println("狗看门");
+    }
+}
diff --git a/day10/src/com/inmind/duotai08/test/Demo09.java b/day10/src/com/inmind/duotai08/test/Demo09.java
index 80d7a1a..a69e864 100644
--- a/day10/src/com/inmind/duotai08/test/Demo09.java
+++ b/day10/src/com/inmind/duotai08/test/Demo09.java
@@ -13,12 +13,12 @@ public class Demo09 {
 
         //以上代码没有多态，所以有50个子类，重复的代码就要编写或封装50次，太繁琐
         //多态写法
-        Employee e1 = new Teacher();
-        Employee e2 = new Assistant();
-        dTWork(e1);
-        dTWork(e2);
-        dTWork(teacher);
-        dTWork(assistant);
+        Employee e1 = new Teacher();//引用数据类型向上转型
+        Employee e2 = new Assistant();//引用数据类型向上转型
+        dTWork(e1);//引用数据类型向上转型
+        dTWork(e2);//引用数据类型向上转型
+        dTWork(teacher);//引用数据类型向上转型
+        dTWork(assistant);//引用数据类型向上转型
     }
 
     //定义一个父类类型接收子类对象，多态的写法