引用计数（retainCount）

#import <Foundation/Foundation.h>
@interface ClassA:NSObject
{
NSString *name;
}
-(void)setName:(NSString*)s;
-(NSString*)name;
-(void)dealloc;

@end

#import "ClassA.h"
@implementation ClassA
-(void)setName:(NSString *)s
{
name=s;
[name retain];
}
-(NSString*)name
{
return name;
}
-(void)dealloc
{
NSLog(@"delloc coling!");
[name release];
[super dealloc];
}
@end

#import <Foundation/Foundation.h>
#import "ClassA.h"
int main(int argc,const char *argv[])
{
NSAutoreleasePool *pool=[[NSAutoreleasePool alloc]init];
NSMutableString *str1=[NSMutableString stringWithString:@"Sam"];
ClassA *classA=[[ClassA alloc]init];
NSLog(@"Str1 count: %x",[str1 retainCount]);

[classA setName:str1];
NSLog(@"str1 count:%x",[str1 retainCount]);

[str1 release];
NSLog(@"str1 count:%x",[str1 retainCount]);
[classA release];
[pool drain];
return  0;
}