w9

w9/Animal.java

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+// 1. 定义Swimmable接口：包含swim()方法
+public interface Swimmable {
+    // 接口方法默认public abstract，可省略修饰符
+    void swim();
+}
+
+// 2. 定义抽象类Animal：包含抽象方法makeSound()
+public abstract class Animal {
+    // 抽象方法：没有方法体，由子类实现
+    public abstract void makeSound();
+}
+
+// 3. Dog类：继承Animal，实现Swimmable接口
+public class Dog extends Animal implements Swimmable {
+    // 实现父类抽象方法makeSound()
+    @Override
+    public void makeSound() {
+        System.out.println("狗叫：汪汪汪！");
+    }
+
+    // 实现Swimmable接口的swim()方法
+    @Override
+    public void swim() {
+        System.out.println("狗在游泳：狗刨式！");
+    }
+}
+
+// 4. Cat类：仅继承Animal，不实现Swimmable接口
+public class Cat extends Animal {
+    // 实现父类抽象方法makeSound()
+    @Override
+    public void makeSound() {
+        System.out.println("猫叫：喵喵喵！");
+    }
+}
+
+// 5. 主类：测试多态调用
+public class AnimalTest {
+    public static void main(String[] args) {
+        // 多态1：父类引用指向子类对象（Animal多态）
+        Animal dog1 = new Dog();
+        Animal cat1 = new Cat();
+
+        System.out.println("=== Animal多态调用makeSound() ===");
+        dog1.makeSound(); // 调用Dog类的makeSound()
+        cat1.makeSound(); // 调用Cat类的makeSound()
+
+        // 多态2：接口引用指向实现类对象（Swimmable多态）
+        Swimmable dog2 = new Dog();
+        System.out.println("\n=== Swimmable多态调用swim() ===");
+        dog2.swim(); // 调用Dog类的swim()
+
+        // 类型转换：将Animal类型的dog1转为Swimmable，调用swim()
+        System.out.println("\n=== 类型转换后调用swim() ===");
+        if (dog1 instanceof Swimmable) { // 安全判断：避免类型转换异常
+            Swimmable swimmableDog = (Swimmable) dog1;
+            swimmableDog.swim();
+        }
+
+        // Cat无法转换为Swimmable，会抛出异常，因此不执行
+        // if (cat1 instanceof Swimmable) {
+        //     Swimmable swimmableCat = (Swimmable) cat1;
+        //     swimmableCat.swim();
+        // }
+    }
+}

w9/Exception.java

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+import java.io.BufferedReader;
+import java.io.FileReader;
+
+public class ScoreAverage {
+    public static void main(String[] args) {
+        BufferedReader br = new BufferedReader(new FileReader("scores.txt"));
+        String line;
+        int sum = 0;
+        int count = 0;
+        while ((line = br.readLine()) != null) {
+            sum += Integer.parseInt(line);
+            count++;
+        }
+        br.close();
+        double avg = (double) sum / count;
+        System.out.println("平均分：" + avg);
+    }
+}

w9/README.md

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+# java
+