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So how comes that they missing out all the cool features like "performSelector", "respondsToSelector"? Sure the whole OOP part may comes from Objective-C (Small

So how comes that they missing out all the cool features like "performSelector", "respondsToSelector"? Sure the whole OOP part may comes from Objective-C (SmallTalk to be precise) but the dynamic parts were poorly executed.

malbs 14y ago
Not to mention the fact that they completely ignored class methods. No, static methods do not count.
- i386 14y ago
  Out of curiosity, why do statics not count for class methods?
  - malbs 14y ago
    class methods are virtual
  - hboon 14y ago
    They are closer to global functions that are attached to classes and don't support inheritance the same way as instance methods. e.g. if a subclass implements a static function with the same signature as its parent, and you call it with the parent class, it invokes the parent class version instead of the subclass version. Class-side methods in Smalltalk are inherited, working with classes (as an object) is analogous to how instance-side methods work with instances (also objects). So e.g implementing and using factory methods are simpler in Smalltalk and similar languages. Edit: grammer and typos.
- jcampbell1 14y ago
  The only difference I know of is that you can override inherited class methods, but not in Java. Is that really an important feature that you use? I suppose you could use it to do "factory" stuff, without an actual factory class.
  - malbs 14y ago
    exactly! Imagine my surprise when I disovered Delphi has class methods too, but they were not copied to C#. I guess most of the time they're not particularly useful, but when you do need to create some factory code, having pure virtual class methods (template methods), is really useful. Downside w/ Delphi is the metaclasses do not implicitly exist - you have to manually define it, eg TMyObjectClass = class of TMyObject; They should just be implicity, when you define a class, the metaclass is defined too. I guess when they first designed it memory constraints were still a consideration
koenigdavidmj 14y ago
Well, they're a lot longer to type, but you can use [1] to get a method (and handle the error to see if it exists) and [2] to call the method on a given object. 1: http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Class.html#getMethod%28java.lang.String,%20java.lang.Class...%29 http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Class... 2: http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/reflect/Method.html#invoke%28java.lang.Object,%20java.lang.Object...%29 http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/refle...
stcredzero 14y ago
(SmallTalk to be precise) Smalltalk to be precise.
aardvark179 14y ago
Java takes its most basic ideas about how OOP is done from the Simula and C++ side, rather from Smalltalk and Objective-C. In that world view you don't ask if something responds to a selector but rather whether it's an instance of a suitable interface. There are still occasions when responsa to/perform is a nice pattern but its often better done with lambdas. Perform also tends to need annoying special casing to optimise. The exception I'd make to that is meta-programming—especially for ORM libraries—where responds to, perform, and lambdas together produce some lovely patterns to marry a schematic to a dynamically generated object hierarchy.

malbs 14y ago

Not to mention the fact that they completely ignored class methods. No, static methods do not count.

i386 14y ago
Out of curiosity, why do statics not count for class methods?
- malbs 14y ago
  class methods are virtual
- hboon 14y ago
  They are closer to global functions that are attached to classes and don't support inheritance the same way as instance methods. e.g. if a subclass implements a static function with the same signature as its parent, and you call it with the parent class, it invokes the parent class version instead of the subclass version. Class-side methods in Smalltalk are inherited, working with classes (as an object) is analogous to how instance-side methods work with instances (also objects). So e.g implementing and using factory methods are simpler in Smalltalk and similar languages. Edit: grammer and typos.
jcampbell1 14y ago
The only difference I know of is that you can override inherited class methods, but not in Java. Is that really an important feature that you use? I suppose you could use it to do "factory" stuff, without an actual factory class.
- malbs 14y ago
  exactly! Imagine my surprise when I disovered Delphi has class methods too, but they were not copied to C#. I guess most of the time they're not particularly useful, but when you do need to create some factory code, having pure virtual class methods (template methods), is really useful. Downside w/ Delphi is the metaclasses do not implicitly exist - you have to manually define it, eg TMyObjectClass = class of TMyObject; They should just be implicity, when you define a class, the metaclass is defined too. I guess when they first designed it memory constraints were still a consideration

koenigdavidmj 14y ago

Well, they're a lot longer to type, but you can use [1] to get a method (and handle the error to see if it exists) and [2] to call the method on a given object. 1: http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Class.html#getMethod%28java.lang.String,%20java.lang.Class...%29 http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Class... 2: http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/reflect/Method.html#invoke%28java.lang.Object,%20java.lang.Object...%29 http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/refle...

stcredzero 14y ago

(SmallTalk to be precise) Smalltalk to be precise.

aardvark179 14y ago

Java takes its most basic ideas about how OOP is done from the Simula and C++ side, rather from Smalltalk and Objective-C. In that world view you don't ask if something responds to a selector but rather whether it's an instance of a suitable interface. There are still occasions when responsa to/perform is a nice pattern but its often better done with lambdas. Perform also tends to need annoying special casing to optimise. The exception I'd make to that is meta-programming—especially for ORM libraries—where responds to, perform, and lambdas together produce some lovely patterns to marry a schematic to a dynamically generated object hierarchy.