java/Animal.java

// 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();
        // }
    }
}