Java，对象编程：获取返回0值的方法

主类

    import javax.swing.JOptionPane;

    public class Shapes {

        static String shape;
        static String circleInput;
        static String c;
        static String r;
        static String t;
        static double radius;

        public static void main(String[] args) {
            // Creation of all three shape objects
            Circle circleSolution = new Circle();
            Rectangle solution2 = new Rectangle(shape, r);
            Triangle solution3 = new Triangle(shape, t);

            String choice = "y";
                // Creation of a while loop which continues when 'choice' is 'y'
            while (choice.equalsIgnoreCase("y")) {
                // Prompts user for a shape or the interger 1 to end the program.
            shape=
                JOptionPane.showInputDialog ("Enter one of the following shapes:"
                    + " circle, rectangle or triangle.");
                    // Converts the String 'shape' into an interger
                if (shape.equalsIgnoreCase("circle")) {
                    shape = c;
                    circleInput = JOptionPane.showInputDialog ("Enter the radius.");
                    radius = Math.abs(Integer.parseInt(circleInput));

                    JOptionPane.showMessageDialog ( 
                    null, "The area of the circle is " + circleSolution.getCircleArea(), "Results", 
                    JOptionPane.PLAIN_MESSAGE);

                    JOptionPane.showMessageDialog ( 
                    null, "The perimeter of the circle is " + circleSolution.getCirclePerimeter(), "Results", 
                    JOptionPane.PLAIN_MESSAGE); 
                }
                else if (shape.equalsIgnoreCase("rectangle")) {
                    shape = r;
                    // Prompts user for pertinent data
                }
                else if(shape.equalsIgnoreCase("triangle")) {
                    shape = t;
                }
            }

public class Circle { 
    // Circle object created
    Shapes circle = new Shapes();
    // Defines variables used in class
    private static String shape;
    private static double radius;
    private static String circleInput;
    private static String c;
    // Constructor for circles, with arguments
    Circle() {
        shape = Shapes.shape;
        radius = Shapes.radius;
        circleInput = Shapes.circleInput;
        c = Shapes.c;
    }
     // Instance method used to return the shape
    public String getShape() {
        return shape;
    }
     // Instance method used to return the value of the circle's radius
    public double getRadius() {
        return radius;
    }
    // Instance method used return the string, circleInput
    public String getCircleInput() {
        return circleInput;
    }
     // Instance method used to return the specific shape
    public String getC() {
       return c;
    }
    double getCircleArea() {
        double circleArea = Math.PI * radius * radius;
        return circleArea;
    }
    double getCirclePerimeter() {
        double circlePerimeter = 2 * Math.PI * radius;
        return circlePerimeter; 
    }   
}

圆形对象类

    import javax.swing.JOptionPane;

    public class Shapes {

        static String shape;
        static String circleInput;
        static String c;
        static String r;
        static String t;
        static double radius;

        public static void main(String[] args) {
            // Creation of all three shape objects
            Circle circleSolution = new Circle();
            Rectangle solution2 = new Rectangle(shape, r);
            Triangle solution3 = new Triangle(shape, t);

            String choice = "y";
                // Creation of a while loop which continues when 'choice' is 'y'
            while (choice.equalsIgnoreCase("y")) {
                // Prompts user for a shape or the interger 1 to end the program.
            shape=
                JOptionPane.showInputDialog ("Enter one of the following shapes:"
                    + " circle, rectangle or triangle.");
                    // Converts the String 'shape' into an interger
                if (shape.equalsIgnoreCase("circle")) {
                    shape = c;
                    circleInput = JOptionPane.showInputDialog ("Enter the radius.");
                    radius = Math.abs(Integer.parseInt(circleInput));

                    JOptionPane.showMessageDialog ( 
                    null, "The area of the circle is " + circleSolution.getCircleArea(), "Results", 
                    JOptionPane.PLAIN_MESSAGE);

                    JOptionPane.showMessageDialog ( 
                    null, "The perimeter of the circle is " + circleSolution.getCirclePerimeter(), "Results", 
                    JOptionPane.PLAIN_MESSAGE); 
                }
                else if (shape.equalsIgnoreCase("rectangle")) {
                    shape = r;
                    // Prompts user for pertinent data
                }
                else if(shape.equalsIgnoreCase("triangle")) {
                    shape = t;
                }
            }

public class Circle { 
    // Circle object created
    Shapes circle = new Shapes();
    // Defines variables used in class
    private static String shape;
    private static double radius;
    private static String circleInput;
    private static String c;
    // Constructor for circles, with arguments
    Circle() {
        shape = Shapes.shape;
        radius = Shapes.radius;
        circleInput = Shapes.circleInput;
        c = Shapes.c;
    }
     // Instance method used to return the shape
    public String getShape() {
        return shape;
    }
     // Instance method used to return the value of the circle's radius
    public double getRadius() {
        return radius;
    }
    // Instance method used return the string, circleInput
    public String getCircleInput() {
        return circleInput;
    }
     // Instance method used to return the specific shape
    public String getC() {
       return c;
    }
    double getCircleArea() {
        double circleArea = Math.PI * radius * radius;
        return circleArea;
    }
    double getCirclePerimeter() {
        double circlePerimeter = 2 * Math.PI * radius;
        return circlePerimeter; 
    }   
}

对于圆的面积和周长，我得到的结果都是0.0。显然，这是不可取的

如果你有任何问题，请尽管问

---

任何和所有的帮助/建议将不胜感激，提前感谢

您的问题是没有在

圆

对象实例中指定半径值。获取输入，解析它，然后调用

getCircleArea（）

似乎您正试图让Circle的构造函数使用主类中的静态radius变量作为半径

我不想解释为什么这不好（完全违背OOP范式），但这不起作用，因为在创建对象之后分配静态变量

 if (shape.equalsIgnoreCase("circle")) {
                    shape = c;
                    circleInput = JOptionPane.showInputDialog ("Enter the radius.");
                    radius = Math.abs(Integer.parseInt(circleInput));
                    circleInput.setRadius(radius); //DO THIS                        

                    JOptionPane.showMessageDialog ( 
                    null, "The area of the circle is " + circleSolution.getCircleArea(), "Results", 
                    JOptionPane.PLAIN_MESSAGE);

---

类的静态成员是默认初始化的

static double radius;

在这种情况下，

半径

初始化为零。这是用来计算面积和周长的

---

另外注意：实例化包含应用程序主方法的类是非常罕见的。

好吧，代码有几个问题。可能是因为您误解了静态和一些面向对象的概念

您的问题：

您的构造函数为空。当您只有一个默认构造函数时，如何期望实例化的对象具有不同的属性

参数化构造函数：

class Circle{
    private double radius;
}

public class Shapes {
    private double radius;
}

class Circle extends Shapes{
    //radius inherited from Shapes now
}

public class Shapes {
    private double radius;
}

class ShapesRunner(){  //Have a designated class for testing
    public static void main(String[] args){
        String circleInput, c, r, t;
        //Your testing for the created shapes.
    }
}

//receive radius from input
circle c = new Circle(radius);
//print c's area and parameter

如果未使用setter设置对象的值，则至少需要一个参数化构造函数来构造对象：

// Constructor for circles, with arguments
Circle(double radius)
{
    radius = this.radius;
    //Your other variables such as c & circleInput variable is not supposed to be here    
}

几乎所有对象的属性都声明为静态。静态变量由同一类的所有对象“共享”，这意味着如果设置该值，它将反映在所有对象中。（准确地说，静态变量属于类而不是单个对象。）当您希望每个圆都有自己的半径，但将其声明为静态时，这没有任何意义

删除所有不必要的静态修改器：

class Circle{
    private double radius;
}

public class Shapes {
    private double radius;
}

class Circle extends Shapes{
    //radius inherited from Shapes now
}

public class Shapes {
    private double radius;
}

class ShapesRunner(){  //Have a designated class for testing
    public static void main(String[] args){
        String circleInput, c, r, t;
        //Your testing for the created shapes.
    }
}

//receive radius from input
circle c = new Circle(radius);
//print c's area and parameter

凭直觉，你的Circle类应该是Shape的一个子类，你没有扩展它

将您的类置于适当的层次结构下：

class Circle{
    private double radius;
}

public class Shapes {
    private double radius;
}

class Circle extends Shapes{
    //radius inherited from Shapes now
}

public class Shapes {
    private double radius;
}

class ShapesRunner(){  //Have a designated class for testing
    public static void main(String[] args){
        String circleInput, c, r, t;
        //Your testing for the created shapes.
    }
}

//receive radius from input
circle c = new Circle(radius);
//print c's area and parameter

您将本地使用的变量（如

circleInput

）与其他实例变量（如radius）混合使用。您还在yourshape类中编写main方法，所有变量都混在一起。你的学校可能希望你把他们分开

在应该声明变量的位置写入变量：

class Circle{
    private double radius;
}

public class Shapes {
    private double radius;
}

class Circle extends Shapes{
    //radius inherited from Shapes now
}

public class Shapes {
    private double radius;
}

class ShapesRunner(){  //Have a designated class for testing
    public static void main(String[] args){
        String circleInput, c, r, t;
        //Your testing for the created shapes.
    }
}

//receive radius from input
circle c = new Circle(radius);
//print c's area and parameter

Java，对象编程：获取返回0值的方法

确保使用setter（如果有）或通过其构造函数设置圆的半径

示例：

class Circle{
    private double radius;
}

public class Shapes {
    private double radius;
}

class Circle extends Shapes{
    //radius inherited from Shapes now
}

public class Shapes {
    private double radius;
}

class ShapesRunner(){  //Have a designated class for testing
    public static void main(String[] args){
        String circleInput, c, r, t;
        //Your testing for the created shapes.
    }
}

//receive radius from input
circle c = new Circle(radius);
//print c's area and parameter

---

我的魔法球是说你犯了一些错误；）为什么使用静态字段？如何传递半径的值。您必须通过方法params获取它，或者重新定义构造函数来获取它。

radius=Shapes.radius形状时调试并检查值。半径

为0。如果随后更改静态值，则圆将不会更新。在知道值后创建圆，或者直接更新圆实例。我相信这比一个魔术球要有用一些……谢谢你的帮助，基本上重写了代码以删除所有静态变量。但是，仍然遇到了一个问题。我在Circle类中创建了一个setRadius方法，但是，我得到了一个错误，它无法在我的main方法中找到符号。public double-setRadius（double-radius）{return radius；}它应该是

public void-setRadius（double-radius）{this.radius=radius；}

您正在为类成员赋值

radius

，而不是检索它谢谢！我真的需要温习一下，当然还要练习。它现在工作：）@Goddard您可以选择要接受的答案（通过单击空心勾号）。但你只能选择一个。因此，您可能希望接受对您最有帮助的解决方案。谢谢！信息量大，很有帮助。我的代码确实帮了我一些可怕的问题。