Java从超类中的子类保存变量

Question

我正在尝试基于以下 UML 类图为分配设计一个 Java 程序，但我一直坚持为 House 和 ApartmentBuilding 类的 create 方法获取 name 和 xPosition 和将其存储在其父类（Building）和接口（@98​​7654328@）中。

可绘制：

import javafx.scene.canvas.GraphicsContext;



 interface Drawable {

   void draw(GraphicsContext canvas);

   public double getXPosition();
   
}

建筑：

import javafx.scene.canvas.GraphicsContext;

public class Building implements Drawable {


    private final String name;

    private final double xPosition;

        public Building(){

            this.name = " ";
            this.xPosition = 0.0;

    }

    public Building(String name, double xPosition){

            this.name = name;
            this.xPosition = xPosition;
    }




    public String getName(){
        return name;
    }


    public void draw(GraphicsContext canvas) {

    }


    public double getXPosition() {
        return xPosition;
    }
    @Override
    public String toString(){
            return "Type... Building:  " + "name= " + name + ", xPosition= " + xPosition + "\n";}
    }

房子：

import javafx.scene.canvas.GraphicsContext;

import java.util.Scanner;

public class House extends Building implements Dwelling  {

    int bedrooms;
    int occupants;

    House(int bedrooms, int occupants){
        this.bedrooms = bedrooms;
        this.occupants = occupants;
    }
    public static House create() {
        Scanner scan = new Scanner(System.in);
        House a;


        System.out.println("Enter name of the House: ");
        String name = scan.nextLine();
        System.out.println("Enter XPosition of the House: ");
        int xPosition = scan.nextInt();
        System.out.println("Enter number of bedrooms: ");
        int bedrooms = scan.nextInt();
        System.out.println("Enter number of occupants: ");
        int occupants = scan.nextInt();

        a = new House(bedrooms, occupants);


        return a;

    }
    public void draw(GraphicsContext canvas){


    }



    @Override
    public String toString(){
        return "House: " + "bedrooms= " + bedrooms + " occupants= " + occupants + "\n" + super.toString();
    }


    @Override
    public int getNumberOfOccupants() {
        return occupants;
    }
}

公寓楼：

import javafx.scene.canvas.GraphicsContext;

import java.util.Scanner;

public class ApartmentBuilding extends HighRise implements Dwelling{

    int occupantsPerFloor;
    int numberOfFloors;

    ApartmentBuilding(int numberOfFloors, int occupantsPerFloor){
        this.occupantsPerFloor = occupantsPerFloor;
        this.numberOfFloors = numberOfFloors;

    }

    public static ApartmentBuilding create() {
        Scanner scan = new Scanner(System.in);
        ApartmentBuilding a;


        System.out.println("Enter name of the Apartment Building: ");
        String name = scan.nextLine();
        System.out.println("Enter XPosition of the Apartment Building: ");
        int xPosition = scan.nextInt();
        System.out.println("Enter number of floors: ");
        int numberOfFloors = scan.nextInt();
        System.out.println("Enter number of occupants per floor: ");
        int occupantsPerFloor = scan.nextInt();

        a = new ApartmentBuilding(numberOfFloors, occupantsPerFloor);


        return a;
    }


    public void draw(GraphicsContext canvas){

    }
    @Override
    public String toString(){

        return "Apartment Building: " + "occupantsPerFloor= " + occupantsPerFloor + "\n" + super.toString() + "\n";
    }

    @Override
    public int getNumberOfOccupants() {
        return 0;
    }
}

我是编程新手，正在努力学习，但不幸的是，我陷入了困境。

Answer 1

这个：

private final String name;
private final double xPosition;

public Building(){
    this.name = " ";
    this.xPosition = 0.0;
}

可能会让你搞砸了。由于name 和xPosition 被声明为final，因此给Building 一个默认构造函数，它不接受任何参数并将name 和xPosition 设置为默认（和无用）值，这意味着除非你采取注意确保子类显式调用另一个超级构造函数，即需要参数并将上述字段的值设置为合理值的超级构造函数，上述字段将证明对您毫无用处。

我建议您取消上面的默认构造函数，而允许 Building 只有一个构造函数，即需要 String 和 double 参数的构造函数：

public Building(String name, double xPosition){
    this.name = name;
    this.xPosition = xPosition;
}

然后确保子类在它们自己的构造函数中调用这个超级构造函数，并传入适当的值。

例如，

public class House extends Building implements Dwelling  {
    private int bedrooms;
    private int occupants;

    House(String name, double xPosition, int bedrooms, int occupants) {
        super(name, xPosition);
        this.bedrooms = bedrooms;
        this.occupants = occupants;
    }
    

这样您可以强制House 实例填充适当的超类字段，这些值可用于House 实例，并在.getName() 或.getXPosition() 被House 实例调用时适当地返回。