题目-单例

Student.h

#import <Foundation/Foundation.h>

@interface Student : NSObject

@property (nonatomic, copy) NSString *name;

- (instancetype)initWithName:(NSString *)name;

//单例：default stand share开头
+ (instancetype)defaultStudent;
@end

Student.m

#import "Student.h"

@implementation Student
static Student *stu = nil;
+ (instancetype)defaultStudent
{
    if (stu == nil) {
        stu = [[Student alloc]init];
    }
    return stu;
}

- (instancetype)init
{
    self = [super init];
    if (self) {
        _name = @"default";
    }
    return self;
}

- (instancetype)initWithName:(NSString *)name
{
    self = [super init];
    if (self) {
        _name = name;
    }
    return self;
}

@end

main.m

#import <Foundation/Foundation.h>
#import "Student.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Student *stu1 = [Student defaultStudent];
        stu1.name = @"小黑";
        Student *stu2 = [Student defaultStudent];
        stu2.name = @"小花";

        Student *stu3 = [Student defaultStudent];
        stu3.name = @"小花3";

        Student *stu4 = [Student defaultStudent];
        stu4.name = @"小花4";
        NSLog(@"%@",stu2.name);
    }
    return 0;
}

输出结果

2015-08-18 16:32:51.805 单例[2425:83353] 小花4