在CanFly接口中，必须使用一个CanFly类型的参数声明速度方法

public interface CanFly {
    void speed(CanFly flyObject);
}

public class Bird implements CanFly {
    private String species;
    private double flyingSpeed;

    public Bird(String species, double flyingSpeed) {
        this.species = species;
        this.flyingSpeed = flyingSpeed;
    }

    @Override
    public void speed(CanFly flyObject) {
        Bird bird = (Bird) flyObject;
        System.out.println("The " + bird.species + " flies at a speed of " + bird.flyingSpeed + " km/h.");
    }
}

public class Airplane implements CanFly {
    private String model;
    private double cruisingSpeed;

    public Airplane(String model, double cruisingSpeed) {
        this.model = model;
        this.cruisingSpeed = cruisingSpeed;
    }

    @Override
    public void speed(CanFly flyObject) {
        Airplane airplane = (Airplane) flyObject;
        System.out.println("The " + airplane.model + " flies at a cruising speed of " + airplane.cruisingSpeed + " km/h.");
    }
}

public class Main {
    public static void main(String[] args) {
        Bird sparrow = new Bird("Sparrow", 50.0);
        Airplane boeing747 = new Airplane("Boeing 747", 900.0);

        sparrow.speed(sparrow);
        boeing747.speed(boeing747);
    }
}