编写一个圆（Circle）类，属性有半径，并提供计算面积和周长的功能。另编写一个测试类TestCircle，要求该测试类中定义一个静态常量circleNumber用来统计当前已经统计圆(Circle对象)的个数。并能计算并输出已有圆(Circle)对象的面积和周长。注意：圆周率对于所有圆都是相等的。这个怎么写啊。。。
 

//Circle.java

public class Circle {
   
    final double PI = 3.14;
   
    static int circleNumber = 0;
   
    private double radius;
   
    public Circle() {
        this.radius = 1.0;
        circleNumber++;
    }
   
    public Circle(double radius) {
        this.radius = radius;
        circleNumber++;
    }

    public double area() {
        return radius*radius*PI;
       
    }
   
    public double perimeter() {
        return 2*PI*radius;
    }

    public double getRadius() {
        return radius;
    }

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

}

//TestCircle.java
public class TestCircle {

    public static void main(String[] args) {
        Circle c1 = new Circle(1.23);
        Circle c2 = new Circle(4.56);
        System.out.println(Circle.circleNumber);

    }

}

兄弟我是个初学者，编的如果有什么错误或不满足要求的，可回复一下，我再修改，共同讨论一起进步嘛！！
import javax.swing.JOptionPane;

public class Circle {
    public static void main(String[] args) {
        int count = 0;
        for (int i = 1; i <= 100; i++) {
            count += 1;
            String n = JOptionPane.showInputDialog("请输入n的值：");
            double radiu = Double.parseDouble(n);
            double pa = 3.14159;
            double area = radiu * radiu * pa;
            double girth = 2 * radiu * pa;
            double m = area * 100000 / 100;
            double x = girth * 100000 / 100;
            System.out.println("圆的面积和周长分别为：" + m + " 和 " + x);
            System.out.println("已统计圆的个数为：" + count);
        }

    }
}

兄弟我是个初学者，编的如果有什么错误或不满足要求的，可回复一下，我再修改，共同讨论一起进步嘛！！
import javax.swing.JOptionPane;

public class Circle {
    public static void main(String[] args) {
        int count = 0;
        for (int i = 1; i <= 100; i++) {
            count += 1;
            String n = JOptionPane.showInputDialog("请输入n的值：");
            double radiu = Double.parseDouble(n);
            double pa = 3.14159;
            double area = radiu * radiu * pa;
            double girth = 2 * radiu * pa;
            double m = area * 100000 / 100;
            double x = girth * 100000 / 100;
            System.out.println("圆的面积和周长分别为：" + m + " 和 " + x);
            System.out.println("已统计圆的个数为：" + count);
        }

    }
}

初学JAVA，一定要先养成面向对象的思想编程，对你将来深入学习JAVA有很大的好处

版主这个貌似有点不对吧。我运行了一下，好像达不到想要的结果呢

其实你只要修改TestCircle就可以了
例如: Circle c1 = new Circle(1.23);//是实例化一个Circle对像c1
      double a = c1.area(); //用对象c1调用方法area()求得面积
      double b = c1.perimeter();//用对象c1调用方法perimeter()求得周长
      int n = Circle.circleNumber //统计创建Circle对象的个数
       System.out.println("Circle c1的面积: " + a);
       System.out.println("Circle c1的周长: " + b);
       System.out.println("已有对象的个数: " +n );

来学习了