这个拷贝构造好奇怪，求大神解释

#include <iostream>//#include <stdlib.h>using namespace std;class Point {public:Point(int xx=0,int yy=0){X=xx;Y=yy;cout<<"Point 构造函数被调用"<<endl;}Point(Point &p);int GetX(){return X;}int GetY(){return Y;}private:int X,Y;};Point::Point(Point &p){X=p.X;Y=p.Y;cout<<"Point拷贝构造函数被调用"<<endl;
}class Line{public:Line(Point xp1,Point xp2);Line(Line &);double GetLen(){return len;}private:Point p1,p2;double len;};Line::Line(Point xp1,Point xp2):p1(xp1),p2(xp2){cout<<"Line构造函数被调用"<<endl;double x=double(p1.GetX()-p2.GetX());double y=double(p1.GetY()-p2.GetY());len=sqrt(x*x+y*y);}Line::Line(Line &L):p1(L.p1),p2(L.p2){cout<<"Line拷贝构造函数被调用"<<endl;len=L.len;}int main(){Point myp1(1,1),myp2(4,5);Line line(myp1,myp2);Line line2(line);cout<<"the length of the line is:";cout<<line.GetLen()<<endl;cout<<"the length of the line2 is:";cout<<line2.GetLen()<<endl;system("pause");}
这个程序结果出现了6个拷贝构造，不知该怎么分析，求大神解释