新增文件推送

w6/Animal.java

@@ -0,0 +1,3 @@
+public abstract class Animal {
+    public abstract void makeSound();
+}

w6/Cat.java

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+public class Cat extends Animal {
+    @Override
+    public void makeSound() {
+        System.out.println("Meow!");
+    }
+}

w6/Dog.java

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+public class Dog extends Animal implements Swimmable {
+    @Override
+    public void makeSound() {
+        System.out.println("Woof!");
+    }
+
+    @Override
+    public void swim() {
+        System.out.println("Dog is swimming");
+    }
+}

w6/Main.java

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+public class Main {
+    public static void main(String[] args) {
+        Animal[] animals = new Animal[2];
+        animals[0] = new Dog();
+        animals[1] = new Cat();
+
+        for (Animal animal : animals) {
+            animal.makeSound();
+            if (animal instanceof Swimmable) {
+                ((Swimmable) animal).swim();
+            }
+        }
+    }
+}

w6/Swimmable.java

@@ -0,0 +1,3 @@
+public interface Swimmable {
+    void swim();
+}