子类调用父类函数
class circle
{
float r;
public circle()
{this.r=1;}
public circle(float r)
{this.r=r;}
float girth()// 周长
{return 3.14f*r*2;}
float area()
{return 3.14f*r*r;}
}
class column extends circle
{
float high;
public column()
{high=2;}
public column(float h)
{high=h;}
float volume() //体积
{return high*area;} ////////请问这里为什么不可以
float barea() //表面积
{return (2*3.14f*r*r+3.14f*r*2*high);}
}