public class Animal{ public Animal(){ System.out.println("I’m an animal."); } } // Bird类是Animal的子类 public class Bird extends Animal{ public Bird(){ System.out.println("I’m a bird."); } public static void main(String[]args){ Bird b = new Bird(); } }

运行这段代码会输出：

I’m an animal.
I’m a bird.

这是因为 `Bird` 类继承了 `Animal` 类，所以在创建 `Bird` 对象时，会先调用父类的构造方法 `Animal()`，输出 `"I’m an animal."`，然后再调用子类的构造方法 `Bird()`，输出 `"I’m a bird."`。

相关问题

public class Animal { String[] animals = {"dog", "cat", "bird", "fish"}; public void printAnimals() { for (String animal : animals) { System.out.println(animal); } }}public class Dog extends Animal { int[] nums = {1, 2, 3, 4}; public void printNums() { for (int num : nums) { System.out.println(num); } }}public class Main { public static void main(String[] args) { Dog dog = new Dog(); dog.printAnimals(); // 输出：dog cat bird fish dog.printNums(); // 输出：1 2 3 4 }}如果这个代码中的数组是在Main中建立该如何解决

可以将数组作为参数传递给Animal和Dog类的构造函数，并在构造函数中初始化数组。代码示例：

public class Animal {
    String[] animals;
    
    public Animal(String[] animals) {
        this.animals = animals;
    }
    
    public void printAnimals() {
        for (String animal : animals) {
            System.out.println(animal);
        }
    }
}

public class Dog extends Animal {
    int[] nums;
    
    public Dog(String[] animals, int[] nums) {
        super(animals);
        this.nums = nums;
    }
    
    public void printNums() {
        for (int num : nums) {
            System.out.println(num);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        String[] animals = {"dog", "cat", "bird", "fish"};
        int[] nums = {1, 2, 3, 4};
        Dog dog = new Dog(animals, nums);
        dog.printAnimals();
        dog.printNums();
    }
}

输出结果与原来的代码相同。

public class TestAnimal { static void showPet(Animal a) { a.eat(); } // static void showCat(Homework7.Cat b){ // b.getName(); // b.play(); // } public static void main(String[] args){ Animal[] animal = new Animal[3]; animal[0] = new Bird(); animal[1] = new Fish(); animal[2] = new Cat(); Animal A = animal[0]; Animal B = animal[1]; Animal C = animal[2]; IPet cat = new Cat(); // // String[] dongwu = new String[3]; // dongwu[0] = A.toString(); // dongwu[1] = B.toString(); // dongwu[2] = C.toString(); // for(int i = 0;i<3;i++){ // System.out.println(); // } showPet(A); showPet(B); showPet(C); cat.play(); cat.getName(); } }我要将Bird、Fish、Cat对象对应数组元素，并用循环输出，要怎么改写

您可以将数组元素的类型改为 Animal，并使用 instanceof 运算符判断元素的类型，然后调用对应的方法。以下是修改后的代码：

public class TestAnimal {
    static void showPet(Animal a) {
        a.eat();
    }
    
    public static void main(String[] args){
        Animal[] animals = new Animal[3];
        animals[0] = new Bird();
        animals[1] = new Fish();
        animals[2] = new Cat();
        
        IPet cat = new Cat();
        
        for (int i = 0; i < animals.length; i++) {
            if (animals[i] instanceof Bird) {
                System.out.println("This is a bird:");
                showPet(animals[i]);
            } else if (animals[i] instanceof Fish) {
                System.out.println("This is a fish:");
                showPet(animals[i]);
            } else if (animals[i] instanceof Cat) {
                System.out.println("This is a cat:");
                showPet(animals[i]);
                cat.play();
                cat.getName();
            }
        }
    }
}

注意，为了调用 Cat 对象的 play() 和 getName() 方法，我们需要将 cat 对象的类型声明为 IPet，而不是 Animal。