当从我的主方法调用时，子类中的toString方法返回零

Question

我已分配使用抽象类作为超类“ Shape”的任务。它具有扩展该类的三个类，即Triangle，Circle和Square。每个类都应计算这些形状的面积和周长。当我在for循环中System.out.println(shapeArray[i].computeArea());时，我的工作正常。但是，当我尝试在该for循环的子类中调用toString方法时，所有内容均返回为“ 0”。感谢您抽出宝贵的时间来帮助我，因为我很困在这里。我觉得我整天都在阅读，重新阅读主题和教科书。我觉得这里只有一个愚蠢的错误，我看不到。

Shape.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;
    }

}

Triangle.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;
    }

}

Circle.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;
    }

}

Rectangle.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;
    }

}

ShapeArray.java

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());
        }
    }
}

输出：

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

您的Triangle.computeArea类方法将从area = this.area;更改为this.area=area;其他类似的课程。

Answer 2

在shapeArray[i].computeArea()之前，您必须先调用for循环shapeArray[i].computePerimeter()和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，因为在打印之前您不调用类实例的周长和面积的计算。但我也建议您检查您的代码，不要使用不必要的变量。]​​>