如何使用复制构造函数

class Circle {

  private double r;

  public Circle(double r) {
    this.r = r;
  }

  public void Circle(double r) {
  }

  double calCircumference() {
    return 2 * Math.PI * r;
  }

  public double calArea() {
    return Math.PI * r * r;
  }
}
class Circle {

  private double r;

  public C