NSString *str = @"123-456-789-000";
    NSArray *arr = [str componentsSeparatedByString:@"-"];
    NSLog(@"%@",arr);
    NSString *str2 = [arr componentsJoinedByString:@""];//数组转为字符串
    NSLog(@"%@",str2);
    
    NSMutableArray *arr2 = [[NSMutableArray alloc]init];
    [arr2 addObject:@"1"];
    [arr2 insertObject:@"3" atIndex:0];
    [arr2 addObject:@"2"];
    NSLog(@"%@",arr2);
    //系统的compara：适合字符串，不适合对象排序
    //2
    NSSortDescriptor *sort1 = [NSSortDescriptor sortDescriptorWithKey:nil ascending:YES];//nil或self
    [arr2 sortUsingDescriptors:[NSArray arrayWithObject:sort1]];//注意可变排序方法和不可排序方法的区别
    
    NSLog(@"%@",arr2);
    //3复杂对象的排序
    Student *s1 = [[Student alloc]init];
    s1.name = @"obanma";
    
    Student *s2 = [[Student alloc]init];
    s2.name = @"jobs";
    
    Student *s3 = [[Student alloc]init];
    s3.name = @"bill";
    
    NSMutableArray *arr3 = [NSMutableArray arrayWithObjects:s1,s2,s3,nil];
    
    NSSortDescriptor *sort2 = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];//kvc
    
    [arr3 sortUsingDescriptors:[NSArray arrayWithObject:sort2]];
    
    for (Student *stu in arr3)
    {
        NSLog(@"stu.name = %@",stu.name);
    }