instance-variables

Ruby class instance variable vs. class variable

由 孤街醉人 提交于 2019-11-26 00:50:29
问题 I read \"When do Ruby instance variables get set?\" but I\'m of two minds when to use class instance variables. Class variables are shared by all objects of a class, Instance variables belong to one object. There\'s not much room left to use class instance variables if we have class variables. Could someone explain the difference between these two and when to use them? Here\'s a code example: class S @@k = 23 @s = 15 def self.s @s end def self.k @@k end end p S.s #15 p S.k #23 I understand

Do declared properties require a corresponding instance variable?

由 自古美人都是妖i 提交于 2019-11-26 00:47:07
问题 Do properties in Objective-C 2.0 require a corresponding instance variable to be declared? For example, I\'m used to doing something like this: MyObject.h @interface MyObject : NSObject { NSString *name; } @property (nonatomic, retain) NSString *name; @end MyObject.m @implementation @synthesize name; @end However, what if I did this instead: MyObject.h @interface MyObject : NSObject { } @property (nonatomic, retain) NSString *name; @end Is this still valid? And is it in any way different to

How do servlets work? Instantiation, sessions, shared variables and multithreading

由 人走茶凉 提交于 2019-11-25 23:55:26
问题 Suppose, I have a webserver which holds numerous servlets. For information passing among those servlets I am setting session and instance variables. Now, if 2 or more users send request to this server then what happens to the session variables? Will they all be common for all the users or they will be different for each user. If they are different, then how was the server able to differentiate between different users? One more similar question, if there are n users accessing a particular

Ruby class instance variable vs. class variable

由 强颜欢笑 提交于 2019-11-25 23:43:52
I read " When do Ruby instance variables get set? " but I'm of two minds when to use class instance variables. Class variables are shared by all objects of a class, Instance variables belong to one object. There's not much room left to use class instance variables if we have class variables. Could someone explain the difference between these two and when to use them? Here's a code example: class S @@k = 23 @s = 15 def self.s @s end def self.k @@k end end p S.s #15 p S.k #23 I understand now, Class Instance Variables are not passed along the inheritance chain! Instance variable on a class:

Should I instantiate instance variables on declaration or in the constructor?

由 半城伤御伤魂 提交于 2019-11-25 22:48:10
问题 Is there any advantage for either approach? Example 1: class A { B b = new B(); } Example 2: class A { B b; A() { b = new B(); } } 回答1: There is no difference - the instance variable initialization is actually put in the constructor(s) by the compiler. The first variant is more readable. You can't have exception handling with the first variant. There is additionally the initialization block, which is as well put in the constructor(s) by the compiler: { a = new A(); } Check Sun's explanation
订阅 instance-variables