创建一个Boat（船）类，它有四个属性：registrationNo（注册 号）、length（长）、manufacturer（制造商）、year（年）， 方法toString返回所有属性的值。 SailBoat（帆船）类和PowerBoat（汽艇）类继承Boat类， SailBoat类还有keelDepth（龙骨深度）和id（帆船编号）属性， PowerBoat还有numberEgines（引擎数）和fuelType（燃料类 型）属性。在SailBoat类和PowerBoat类重写toString方法（要 求调用父类方法）。 分别创建三个类的对象，使用setter或构造方法赋值，输出其所 有属性值。java

以下是 Boat 类的实现：

public class Boat {
    private String registrationNo;
    private double length;
    private String manufacturer;
    private int year;

    public Boat(String registrationNo, double length, String manufacturer, int year) {
        this.registrationNo = registrationNo;
        this.length = length;
        this.manufacturer = manufacturer;
        this.year = year;
    }

    public String toString() {
        return "Registration No: " + registrationNo + "\nLength: " + length + "\nManufacturer: " + manufacturer + "\nYear: " + year;
    }
}

以下是 SailBoat 类的实现：

public class SailBoat extends Boat {
    private double keelDepth;
    private int id;

    public SailBoat(String registrationNo, double length, String manufacturer, int year, double keelDepth, int id) {
        super(registrationNo, length, manufacturer, year);
        this.keelDepth = keelDepth;
        this.id = id;
    }

    public String toString() {
        return super.toString() + "\nKeel Depth: " + keelDepth + "\nID: " + id;
    }
}

以下是 PowerBoat 类的实现：

public class PowerBoat extends Boat {
    private int numberEngines;
    private String fuelType;

    public PowerBoat(String registrationNo, double length, String manufacturer, int year, int numberEngines, String fuelType) {
        super(registrationNo, length, manufacturer, year);
        this.numberEngines = numberEngines;
        this.fuelType = fuelType;
    }

    public String toString() {
        return super.toString() + "\nNumber of Engines: " + numberEngines + "\nFuel Type: " + fuelType;
    }
}

以下是测试代码：

public class BoatTest {
    public static void main(String[] args) {
        Boat boat = new Boat("A1234", 10.5, "Boat Company", 2022);
        System.out.println(boat);

        SailBoat sailBoat = new SailBoat("B5678", 15.0, "Sailboat Company", 2022, 3.0, 1);
        System.out.println(sailBoat);

        PowerBoat powerBoat = new PowerBoat("C9101", 20.0, "Powerboat Company", 2022, 2, "Gasoline");
        System.out.println(powerBoat);
    }
}

输出结果如下：

Registration No: A1234
Length: 10.5
Manufacturer: Boat Company
Year: 2022

Registration No: B5678
Length: 15.0
Manufacturer: Sailboat Company
Year: 2022
Keel Depth: 3.0
ID: 1

Registration No: C9101
Length: 20.0
Manufacturer: Powerboat Company
Year: 2022
Number of Engines: 2
Fuel Type: Gasoline