java - 为什么我的 setter 和 getter 方法不起作用？

Question

我一直在查看我的源代码，但无法弄清楚它有什么问题。我认为问题出在 Circle 类上。当我从DriverCircle 类给了我错误的输出。对于 getDiameter，它只是打印出 0。

public class Circle{
    private double radius;  
    private double pi;
    private double diameter;
    private double circumference;
    private double area; 

    public Circle(){
        pi = Math.PI;
        radius = 0;
    }

    public Circle(double radius){
        this.radius = radius;
    }
    public void setDiameter(){
        diameter = (2 * radius);
    }
    public double getDiameter(){
        //diameter = 2 * radius;
        return diameter;
    }
    public void setCircumference(){
        circumference = (2 * pi * radius);
    }
    public double getCircumference(){
        //circumference = 2 * pi * radius;
        return circumference;
    }
    public double getArea(){
        //area = pi * Math.pow(radius, 2);
        return area;
    }
    public void setArea(){
        area = (pi * Math.pow(radius, 2));
    }
    public void setRadius(double radius){
        this.radius = radius;
    }
    public double getRadius(){
        return radius;
    }
    public String toString(){
        return "The radius is " + radius;
    }
}

---

(测试人员)...

import java.util.Scanner;

public class CircleDriver {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        System.out.println("Please enter the radius: ");
        Circle[] circles = new Circle[10];
        Circle objectCircle = new Circle();
        objectCircle.setRadius(input.nextDouble());


        circles[1] = new Circle();
        circles[2] = new Circle(2.0);
        circles[3] = new Circle(3.5);
        circles[4] = new Circle(5.0);
        circles[5] = new Circle(0.0);
        circles[6] = new Circle(15);
        circles[7] = new Circle(25);
        circles[8] = new Circle(-7);
        circles[9] = new Circle(-10.0);

        System.out.println("Initial call to toString():");
        for (Circle c : circles)
            {System.out.println("\t" + c);}

        System.out.println("Call to getRadius (should be same as above):");
        for (Circle r : circles)
            {if (r != null)
                {System.out.println("\t" + r.getRadius());}}

        System.out.println("Call to getDiameter (should be twice the value shown above):");
        for (Circle d : circles)
            {if (d != null)
                {System.out.println("\t" + d.getDiameter());}}

        System.out.println("Calls to getCircumference:");
        System.out.println("\tShould be 2 * PI:  " + circles[1].getCircumference());
        System.out.println("\tShould be 0.0:  " + circles[5].getCircumference());

        System.out.println("\nCall to getArea:");
        System.out.println("\tShould be PI:  " + circles[1].getArea());
        System.out.println("\tShould be 0.0:  " + circles[5].getArea());

        System.out.println("Testing out the setRadius method:");
        for (int i = 0; i < circles.length / 2; i++)
            {if (circles[i] != null)
                {circles[i].setRadius(i);}}

        System.out.println("Call to toString after setting the first half of the objects:");
        for (Circle c : circles)
            {System.out.println("\t" + c);}
    }
}

Answer 1

您的 setter 方法应该有参数并使用参数来设置字段。否则它们实际上不是 setter 方法。您当前的 setter 方法应该全部丢弃，也许 setRadius(...) 除外，并且大部分计算都在各自的 getter 方法中完成。

即不

public void setCircumference(){
    circumference = (2 * pi * radius);
}

public double getCircumference(){
    //circumference = 2 * pi * radius;
    return circumference;
}

而是

public double getCircumference(){
    return 2 * Math.PI * radius;
}