类的三大特性之一：继承[入门程序示例]

 1 #import <Foundation/Foundation.h>
 2 #import "Location.h"
 3 #import "Rectangle.h"
 4 
 5 int main(int argc, const char * argv[]) {
 6     @autoreleasepool {
 7         Location *loc=[[Location alloc]init];
 8         [loc setX:12];      //因为使用了@propery和@synthesize，所以可以用setX给x赋值
 9         [loc setY:15];
10         [loc description];
11         Rectangle *rec=[[Rectangle alloc]init];
12         [rec setX:190];
13         [rec setY:210];
14         [rec setHeight:120];
15         [rec setWidth:150];
16         [rec description];
17     }
18     return 0;
19 }

1 #import <Foundation/Foundation.h>
2 
3 @interface Location : NSObject
4 @property int x;
5 @property int y;
6 -(void)description;
7 @end

1 #import "Location.h"
2 
3 @implementation Location
4 -(void)description{
5     NSLog(@"x=%d,y=%d",x,y);
6 }
7 @synthesize x,y;
8 @end

1 #import "Location.h"
2 
3 @interface Rectangle : Location
4 @property int height;
5 @property int width;
6 -(void)description;
7 @end

1 #import "Rectangle.h"
2 
3 @implementation Rectangle
4 @synthesize height,width;
5 -(void)description{
6     NSLog(@"x=%d,y=%d,height=%d,width=%d",super.x,super.y,self.height,self.width);
7     //super.x是父类中的x，self.height是本类中的height，“self.”可以省略
8 }
9 @end