public?class?Circle?{
private?double?r;
public?Circle(double?r)?{
this.r?=?r;
}
public?Circle()?{
}
public?double?calC(){
return?2*Math.PI*r;
}
public?double?calA(){
return?Math.PI*r*r;
}
public??void?displayXY(double?r,?double?t){
double?x?=?r*Math.cos(t);
double?y?=?r*Math.sin(t);
System.out.println("x?=?"?+?x?+",?"+"y?=?"+y);
}
}