ios - Meaning of warning "Class implementation may not have super class" -

i have created basic objective-c class.

myclass.h

@interface myclass: nsobject @end 

myclass.m

#import "myclass.h" @interface myclass() @end  @implementation myclass: nsobject  {     nsmutablearray* _myarray; } @end 

xcode showing following warning on @implementation line:

class implementation may not have super class

the warning goes away if remove nsmutablearray* _myarray; line.

what warning mean? doing wrong?

delete nsobject in implementation part. super class has specified in interface.

@implementation myclass {     nsmutablearray* _myarray; } @end