错误：ArrayList 类型中的 add(Shape) 方法<Shape>不适用于参数 (Shape.Rectangle)

Question

我正在尝试向 ArrayList 添加新形状，但收到此错误消息： ArrayList 类型中的方法 add(Shape) 不适用于参数 (Shape.Rectangle)

Shape.Rectangle 是我制作的自定义类。它的参数是矩形（字符串名称，双倍长度，双倍宽度）。

对于圆形和三角形，我也收到此错误。

如果我将 ArrayList 类型更改为 Object 而不是 Shape，则 create() 方法将起作用。但是，方法 display() 停止工作。

我的代码如下：

public static void create(ArrayList<Shape> list) throws FileNotFoundException {
    // Create shape objects using data from an input file
    File dataFile = new File("./src/shape/dataFile.txt");
    Scanner scan = new Scanner(dataFile);
    
    while (scan.hasNextLine()) {
        String shapeType = scan.nextLine();
        if (shapeType.equals("Rectangle")) {
            list.add(new Rectangle(scan.nextLine(), scan.nextDouble(), scan.nextDouble()));
        }
        else if (shapeType.equals("Circle")) {
            list.add(new Circle(scan.nextLine(), scan.nextDouble()));
        }
        else if (shapeType.equals("Triangle")) {
            list.add( new Triangle(scan.nextLine(), scan.nextDouble(), scan.nextDouble(), scan.nextDouble()));
        }
        
    }
    scan.close();
}

public static void display(ArrayList<Shape> list) {
    
    for (int i = 0; i < list.size(); i++) {
        Shape shape = list.get(i);
        String name = shape.getName();
        Double area = shape.area();
        
        System.out.println(name);
        System.out.println(area);
        }
    }

如果我将 ArrayList 类型更改为 Object 而不是 Shape，则 create() 方法将起作用。但是，当我尝试 getName() 和 area() 时，我在 display() 方法中收到错误。

编辑： 形状和矩形的代码是：

abstract class Shape {

/**
 * The name of this shape
 */
private String name;

/**
 * Default constructor
 * Creates a Shape instance with a default name such as "Shape"
 */
public Shape() {
    this.name = "Shape";
}

/**
 * Second constructor
 * Given a name, creates a Shape instance with the name
 * @param name Name of the new shape
 */
public Shape(String name) {
    this.name = name;
}

/**
 * Retrieves the name of this shape
 * @return Returns the name of shape
 */
public String getName() {
    return name;
}

/**
 * Given a name, changes the name of this shape to the new name
 * @param newName New name of the shape
 */
public void setName(String newName) {
    this.name = newName;
}

/**
 * Returns the area of this shape
 * @return Return of the area of shape
 */
abstract double area();

/**
 * Compares this with some other object
 * This method overrides the java equals method
 * @param obj A reference to some other object
 * @return true if some other object is equal to this shape, false otherwise
 */
public boolean equals(Object obj) {
    if(obj == this.name) {
        return true;
    }
    else {
        return false;
    }
}

/**
 * Represents this shape as a string literal
 * This method overrides the Java toString method
 * @return A string representation of the shape
 */
public String toString() {
    return this.getClass().getSimpleName() + ": " + this.name;
}



/**
 * Rectangle Subclass
 */
public static class Rectangle {
    
    /**
     * Instance variables
     * Name, length, and width of shape.
     */
    private String name;
    private Double length, width;
    
    /**
     * Default Constructor
     * Creates a default rectangle instance.
     */
    public Rectangle() {
        this.name = "Rectangle";
        this.length = 1.0;
        this.width = 1.0;
    }
    
    /**
     * Second Constructor
     * Given a name, a length, and a width, creates a rectangle instance with the name, the length, and the width.
     * @param name, length, width Create a rectangle with these arguements
     */
    public Rectangle(String name, Double length, Double width) {
        this.name = name;
        this.length = length;
        this.width = width;
    }
    
    /**
     * getName
     * Returns the name of this rectangle
     * @return name Return name of this rectangle
     */
    public String getName() {
        return name;
    }
    
    /**
     * setName
     * Given a name, replace the name of this rectangle
     * @param newName Name to replace the original name of this rectangle
     */
    public void setName(String newName) {
        this.name = newName;
    }
    
    /**
     * getLength
     * Returns the length of this rectangle
     * @return length
     */
    public Double getLength() {
        return length;
    }
    
    /**
     * setLength
     * Given a length, changes the length of this rectangle to the new length.
     * @param newLength
     */
    public void setLength(Double newLength) {
        this.length = newLength;
    }
    
    /**
     * getWidth
     * Returns the width of this rectangle
     * @Return width
     */
    public Double getWidth() {
        return width;
    }
    
    /**
     * setWidth
     * Given a width, changes the width of this rectangle to the new width
     * @param newWidth
     */
    public void setWidth(Double newWidth) {
        this.width = newWidth;
    }
    
    /**
     * Area
     * Returns the area of this rectangle
     * @return area
     */
    public Double area() {
        double area = this.length * this.width;
        return area;
    }
    
    /**
     * Equals
     * Compares this rectangle with some other object.
     * @param obj Reference object to compare to
     * @return true if some other object is equal to this rectangle, false otherwise
     */
    public boolean equals(Object obj) {
        
        if(obj == this.name) {
            return true;
        }
        else {
            return false;
        }
    }
    
    /**
     * toString
     * Represents this rectangle as a string literal.
     * @return A string representation of this rectangle
     */
    public String toString() {
        return this.getClass().getSimpleName() + ": " + this.name;
    }
}

Answer 1

该列表需要

Shape

类的参数，但是您正在传递

Rectangle

。 您可能想要创建

Rectangle

、

Circle

和

Triangle

类来继承

Shape

。