Java：我可以要求子类定义属性值吗？

abstract class Animal {
    protected String name;
    
    public abstract void sound();
}

class Dog extends Animal {
    public Dog(String name) {
        this.name = name;
    }
    
    public void sound() {
        System.out.println(name + " barks");
    }
}

class Cat extends Animal {
    public Cat(String name) {
        this.name = name;
    }
    
    public void sound() {
        System.out.println(name + " meows");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal dog = new Dog("Buddy");
        dog.sound();  // Output: Buddy barks
        
        Animal cat = new Cat("Whiskers");
        cat.sound();  // Output: Whiskers meows
    }
}

interface Shape {
    double getArea();
}

class Circle implements Shape {
    private double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    public double getArea() {
        return Math.PI * radius * radius;
    }
}

class Rectangle implements Shape {
    private double width;
    private double height;
    
    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    
    public double getArea() {
        return width * height;
    }
}

public class Main {
    public static void main(String[] args) {
        Shape circle = new Circle(5);
        System.out.println("Circle area: " + circle.getArea());  // Output: Circle area: 78.53981633974483
        
        Shape rectangle = new Rectangle(4, 6);
        System.out.println("Rectangle area: " + rectangle.getArea());  // Output: Rectangle area: 24.0
    }
}