從主方法調用時，子類中的 toString 方法返回零

Question

我有任務使用抽象類作為超類“形狀”。 它具有擴展該類的三個類，Triangle、Circle 和 Square。 每個類都應該計算這些形狀的面積和周長。 當我System.out.println(shapeArray[i].computeArea()); 在 for 循環中。 但是當我嘗試從該 for 循環中的子類調用 toString 方法時，一切都返回為“0”。 我感謝任何人花時間提供幫助，因為我很困在這里。 我覺得我一整天都在閱讀和重讀主題和教科書。 我覺得這里有一些我看不到的愚蠢錯誤。

形狀.java

public class Circle extends Shape {

    private double radius;
    final private double PI = 3.14159;
    private double circumfrence;
    private double area;

    Circle(double radius) {

        this.radius = radius;
    }

    @Override
    public double computeArea() {
        double radSquared = radius * radius;
        double area = PI * radSquared;
        return area;
    }

    @Override
    public double computePerimeter() {
        circumfrence = 2 * PI * radius;
        return circumfrence;
    }

    @Override
    public String toString() {
        return  "Area of Circle: " +area + "\nCircumfrence of Circle: " + circumfrence;
    }

}

三角形.java

public class Triangle extends Shape {

    private double side1;
    private double side2;
    private double side3;
    private double area;
    private double perimeter;


    Triangle (double side1, double side2, double side3) {
        this.side1 = side1;
        this.side2 = side2;
        this.side3 = side3;
    }

    @Override
    public double computeArea() {
          double s =(side1 + side2 + side3) / 2;
          double area= Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
          area = this.area;
          return area;
    }

    @Override
    public double computePerimeter() {
        perimeter = side1 + side2 + side3;
        return perimeter;
    }

    @Override
    public String toString() {
        return "Area of Triangle: " + area+ "\nPerimeter of Triangle: " + perimeter;
    }

}

圓環.java

public class Circle extends Shape {

    private double radius;
    final private double PI = 3.14159;
    private double circumfrence;
    private double area;

    Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double computeArea() {
        double radSquared = radius * radius;
        double area = PI * radSquared;
        return area;
    }

    @Override
    public double computePerimeter() {
        circumfrence = 2 * PI * radius;
        return circumfrence;
    }

    @Override
    public String toString() {
        return  "Area of Circle: " +area + "\nCircumfrence of Circle: " + circumfrence;
    }

}

矩形.java

public class Rectangle extends Shape {

    private double length;
    private double height;
    private double sumOfLength;
    private double sumOfHeight;
    private double area;
    private double perimeter;

    Rectangle(double length, double height) {
        this.height = height;
        this.length = length;
    }

    @Override
    public double computeArea() {
        area = (length * height);
        return area;
    }

    @Override
    public double computePerimeter() {
        sumOfLength = length * 2;
        sumOfHeight = height * 2;
        perimeter = sumOfLength + sumOfHeight;
        return perimeter;
    }

    @Override
    public String toString() {
        return "Area of Rectangle: " +area + "\nPerimeter of Rectangle: " + perimeter;
    }

}

形狀數組

public class ShapeArray {

    public static void main(String [] args) {

        Shape shapeArray[] = new Shape[3];

        Circle circ = new Circle(9);
        Rectangle rect = new Rectangle(10, 6);
        Triangle tri = new Triangle(6, 8, 12);

        shapeArray[0] = circ;
        shapeArray[1] = rect;
        shapeArray[2] = tri;

        for (int i = 0; i <= 2; i++) {
            System.out.println(shapeArray[i].toString());
        }
    }
}

輸出：

Area of Circle: 0.0
Circumfrence of Circle: 0.0
Area of Rectangle: 0.0
Perimeter of Rectangle: 0.0
Area of Triangle: 0.0
Perimeter of Triangle: 0.0

Answer 1

你的類Triangle.computeArea方法改變了 from area = this.area; 到this.area=area; 其他班這樣。

Answer 2

您必須在shapeArray[i].toString()之前調用 for 循環shapeArray[i].computeArea()和shapeArray[i].computePerimeter() shapeArray[i].toString() 。

在ShapeArray.java 中

//other code

for (int i = 0; i <= 2; i++) {
    shapeArray[i].computeArea();
    shapeArray[i].computePerimeter()
    System.out.println(shapeArray[i].toString());
}

//other code

它打印 0，因為您在打印之前沒有調用類實例的周長和面積計算。 但我也建議檢查您的代碼，它沒有使用不必要的變量。