java编程问题，，求高手帮忙解决下万分感谢，，程序能编译但运行不成功，，请高手指点下，程序如下

Question

程序如下：
class Point {
double x;
double y;
Point(double x1,double y1) {
x = x1;
y = y1;
}

double getX() {
return x;
}
double getY() {
return y;
}
void setX(double i) {
x = i;
}
void setY(double i) {
y = i;
}
}

class Circle {
Point o;
double radius;
Circle(Point p,double r) {
o = p;
radius = r;
}
Circle(double r) {
Point o = new Point(0.0,0.0);
radius = r;
}
Point getO() {
return o;
}
void setO(double x,double y) {
o.setX(x);
o.setY(y);
}
double getRadius() {
return radius;
}
void setRadius(double r) {
radius = r;
}

boolean contains(Point p) {
double x = p.getX() - o.getX();
double y = p.getY() - o.getY();
if(x * x - y * y > radius * radius)
return false;
else return true;
}
double area() {
return 3.14 * radius * radius;
}
}

public class TestCircle {
public static void main(String[] args) {
Circle c1 = new Circle(new Point(1.0,2.0),2.0);
Circle c2 = new Circle(5.0);
System.out.println("c1 : (" + c1.getO().getX() + "," +
c1.getO().getY() + ")," + c1.getRadius());
System.out.println("c2 : (" + c2.getO().getX() + "," +
c2.getO().getY() + "," + c2.getRadius());
System.out.println("c1 area = " + c1.area());
System.out.println("c2 area = " + c2.area());
c1.setO(5,6);
c2.setRadius(9.0);
System.out.println("c1 : (" + c1.getO().getX() + "," +
c1.getO().getY() + "}," + c1.getRadius());
System.out.println("c2 : (" + c2.getO().getX() + "," +
c2.getO().getY() + "}," + c2.getRadius());
System.out.println("c1 area = " + c1.area());
System.out.println("c2 area = " + c2.area());

Point p1 = new Point(5.2,6.3);
System.out.println(c1.contains(p1));
System.out.println(c1.contains(new Point(10.0,9.0)));

}
}

Answer 1

class Circle中的构造方法：
Circle(double r) {
Point o = new Point(0.0,0.0);
radius = r;
}

Point o = new Point(0.0,0.0);这句把前面的Point去掉，就可以了。或者更清楚地，把这句话改为this.o = new Point(0.0,0.0);

因为如果你加了这个Point，这句话的意思只是把构造方法中的这个局部变量o给赋值了，
而整个class中的变量Point o，这个o没有被初始化，指向null，所以在后面的getO()方法被调用的时候，返回的是这个class Circle的global变量o，其实没有被赋值，所以会出错，NullPointerException

Answer 2

把构造函数Circle(double r) {
Point o = new Point(0.0,0.0);
radius = r;
}
的Point去掉就行了。。
改成
Circle(double r) {
o = new Point(0.0,0.0);
radius = r;
}

Answer 3

请贴出错误信息。。。