1. @interface Circle : NSObject
   
2. {
   
3.     // 半径
   
4.     double _radius;
   
5.     // 圆心
   
6.     Point2D * _point;
   
7. }
   
8. 
   
9. //判断跟其他圆是否重叠
   
10. //返回值是BOOL类型的 一般方法名都已is开头
    
11. - (BOOL)isInteractWithOther:(Circle *)other;
    
12. 
    
13. //判断两个圆是否重叠
    
14. + (BOOL)isInteractBerweenCircle1:circle1 andCircle2:circle2;
    
15. 
    
16. 
    
17. // _radius geter setter
    
18. - (void)setRadius:(double)radius;
    
19. - (double)radius;
    
20. 
    
21. //_point setter getter
    
22. - (void)setPoint:(Point2D *)point;
    
23. - (Point2D *)point;
    
24. @end
    
25. 
    
26. @implementation Circle
    
27. //_radius setter getter
    
28. - (void)setRadius:(double)radius
    
29. {
    
30.     _radius = radius;
    
31. }
    
32. - (double)radius
    
33. {
    
34.     return _radius;
    
35. }
    
36. 
    
37. //_point setter getter
    
38. - (void)setPoint:(Point2D *)point
    
39. {
    
40.     _point = point;
    
41. }
    
42. - (Point2D *)point
    
43. {
    
44.     return _point;
    
45. }
    
46. 
    
47. //判断跟其他圆是否重叠
    
48. //返回值是BOOL类型的 一般方法名都已is开头
    
49. - (BOOL)isInteractWithOther:(Circle *)other
    
50. {
    
51.     //如果两个圆心的距离<两个圆的半径，重叠
    
52.     double distance = [[self point] distanceWithOther:[other point]];
    
53.     double radiusSum =[self radius] + [other radius];
    
54.     return distance < radiusSum;
    
55. }
    
56. 
    
57. //判断两个圆是否重叠
    
58. + (BOOL)isInteractBerweenCircle1:circle1 andCircle2:circle2
    
59. {
    
60.     return [circle1 isInteractWithOther:circle2];
    
61. }
    
62. @end
    

复制代码

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大家看最后两个方法，我改成这样：
- (BOOL)isInteractWithOther:(Circle *)other
{
       return [Circle * isInteractBerweenCircle1:self andCircle2:other];
}
+ (BOOL)isInteractBerweenCircle1:circle1 andCircle2:circle2
{
    //如果两个圆心的距离<两个圆的半径，重叠
    double distance = [[circle1 point] distanceWithOther:[circle2 point]];
    double radiusSum =[circle1 radius] + [circle2 radius];
    //
    return distance < radiusSum;
}
在这里
return [Circle * isInteractBerweenCircle1:self andCircle2:other];
提示我isInteractBerweenCircle1andCirle2没声明，但是在@interface里面不是声明了么   ，哪个不算么

方法声明：
+ (BOOL)isInteractBerweenCircle1:（Circle *）circle1 andCircle2:（Circle *）circle2;