Java 求圆的半径、直径、面积和周长

所以我还是一个编程新手，我不知道这是否都是正确的，但我试图找到一个给定半径的圆的面积周长

到目前为止，我有：

public class Circle  {

   private double radius;

   public Circle(double r) {

   }

   public double getRadius()  {
      return radius;
   }

   public void setRadius(double r)  {
   }

   public double diameter()  {
      double diameter = radius * radius;
      return diameter;
   }

   public double area()   {
      double area = Math.PI * (radius * radius);
      return area;
   }

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

我还有另一部分

public class CircleTest {
   private static void circleTest (int r) {
      Circle circleTest = new Circle(-2);
      System.out.printf("Parameter: %d%n", r);
      System.out.printf("Radius: %.1f %n", circleTest.getRadius());
      System.out.printf("Diameter: %.1f %n", circleTest.diameter());
      System.out.printf("Area: %.1f %n", circleTest.area());
      System.out.printf("Circumference: %.1f %n", circleTest.circumference());
   }

   public static void main(String[] args) {

   }
}

---

我不知道这是否正确，但它编译得很好，但当我运行它时，它不会打印出任何内容。我做错了什么？

在Java语言中，当您使用Java解释器执行一个类时，运行时系统通过调用该类的main（）方法启动

您应该在这个块中放入一些代码

   public static void main(String[] args) {

   }

---

代码几乎没有错误。一定是这样

public class Circle  {

   private double radius;

   public Circle(double r) {
    radius = r;

   }

   public double getRadius()  {
      return radius;
   }

   public void setRadius(double r)  {
   }

   public double diameter()  {
      double diameter = radius * radius;
      return diameter;
   }

   public double area()   {
      double area = Math.PI * (radius * radius);
      return area;
   }

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

public class CircleTest {
      public static void main(String[] args) {
         Circle circleTest = new Circle(-2);
              System.out.printf("Parameter: %d%n", r);
              System.out.printf("Radius: %.1f %n", circleTest.getRadius());
               System.out.printf("Diameter: %.1f %n", circleTest.diameter());
              System.out.printf("Area: %.1f %n", circleTest.area());
              System.out.printf("Circumference: %.1f %n", circleTest.circumference());
           }
        }

主课必须是这样的

public class Circle  {

   private double radius;

   public Circle(double r) {
    radius = r;

   }

   public double getRadius()  {
      return radius;
   }

   public void setRadius(double r)  {
   }

   public double diameter()  {
      double diameter = radius * radius;
      return diameter;
   }

   public double area()   {
      double area = Math.PI * (radius * radius);
      return area;
   }

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

public class CircleTest {
      public static void main(String[] args) {
         Circle circleTest = new Circle(-2);
              System.out.printf("Parameter: %d%n", r);
              System.out.printf("Radius: %.1f %n", circleTest.getRadius());
               System.out.printf("Diameter: %.1f %n", circleTest.diameter());
              System.out.printf("Area: %.1f %n", circleTest.area());
              System.out.printf("Circumference: %.1f %n", circleTest.circumference());
           }
        }

---

您犯的错误1）您的代码必须在main方法中。2）构造函数参数必须设置为类变量。

为什么要传递负半径，为什么构造函数内部为空？你认为radius是如何在你的程序中得到一个值的？你的

main

方法是空的，这意味着它不会做任何事情。你的直径是r^2。。。如果你不懂数学，编程并不重要。