diff --git a/6.1.txt b/6.1.txt
new file mode 100644
index 0000000..0e98992
--- /dev/null
+++ b/6.1.txt
@@ -0,0 +1,3 @@
+public abstract class Animal {
+    public abstract void makeSound();
+}
\ No newline at end of file
diff --git a/6.2.txt b/6.2.txt
new file mode 100644
index 0000000..26c5a27
--- /dev/null
+++ b/6.2.txt
@@ -0,0 +1,3 @@
+public interface Swimmable {
+    void swim();
+}
\ No newline at end of file
diff --git a/6.3.txt b/6.3.txt
new file mode 100644
index 0000000..d7f462e
--- /dev/null
+++ b/6.3.txt
@@ -0,0 +1,11 @@
+public class Dog extends Animal implements Swimmable {
+    @Override
+    public void makeSound() {
+        System.out.println("狗：汪汪汪");
+    }
+
+    @Override
+    public void swim() {
+        System.out.println("狗会游泳");
+    }
+}
\ No newline at end of file
diff --git a/6.4.txt b/6.4.txt
new file mode 100644
index 0000000..af09a09
--- /dev/null
+++ b/6.4.txt
@@ -0,0 +1,6 @@
+public class Cat extends Animal {
+    @Override
+    public void makeSound() {
+        System.out.println("猫：喵喵喵");
+    }
+}
\ No newline at end of file
diff --git a/6.5.txt b/6.5.txt
new file mode 100644
index 0000000..865dd33
--- /dev/null
+++ b/6.5.txt
@@ -0,0 +1,15 @@
+public class TestAnimal {
+    public static void main(String[] args) {
+        Animal dog = new Dog();
+        Animal cat = new Cat();
+
+        dog.makeSound();
+        cat.makeSound();
+
+        // 向下转型调用游泳方法
+        if (dog instanceof Swimmable) {
+            Swimmable swimmable = (Swimmable) dog;
+            swimmable.swim();
+        }
+    }
+}
\ No newline at end of file