lazy-evaluation

I am using JSON to parse an online xml document and also 2 methods for lazy image loading. Below is my source code, explanation and my problem: Explanation: Method 1: Use AsyncTask and line imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView); inside the adapter. Method 2: Not use AsyncTask and use the rest of the try-catch block and NOT the line imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView); The problems: Method 1: The images are displayed on the emulator and the loading is pretty fast, but they fail to display on a

I have a scenario where I have some objects that need to take in references from each other. The only way I can get this to compile is to use lazy class A(b:B) class B(a:A) lazy val a:A = new A(b) lazy val b:B = new B(a) I can do the same thing using some actors, and get it to compile also abstract class Message case class Message1 extends Message case class Message2 extends Message class Actor1(otherActor:Actor) extends Actor { def act() { loop { react { case Message1 => println("received message1") otherActor ! Message2 case _ => } } } } class Actor2(otherActor:Actor) extends Actor { def act

From my understanding, lazy evaluation is the arguments are not evaluated before they are passed to a function, but only when their values are actually used. But in a haskell tutorial, I see an example. xs = [1,2,3,4,5,6,7,8] doubleMe(doubleMe(doubleMe(xs))) The author said an imperative language would probably pass through the list once and make a copy and then return it. Then it would pass through the list another two times and return the result. But in a lazy language, it would first compute doubleMe(doubleMe(doubleMe(1))) This will give back a doubleMe(1) , which is 2 . Then 4 , and

I have one django model which needs to do some processing referring the custom user model. I can't work with the class of this model at class loading time because the loading order of the classes is unknown. So I need to add some class attributes at runtime, at the moment I'm adding them in the __init__ or __new__ like: def __new__(cls, *args, **kwargs): # hack to avoid INSTALLED_APPS initialization conflicts. # get_user_model() can't be called from this module at class loading time, # so some class attributes must be added later. # Metaclasses could me more appropiate but I don't want to

Am I right understanding that def is evaluated every time it gets accessed lazy val is evaluated once it gets accessed val is evaluated once it gets into the execution scope? Yes, though for the 3rd one I would say "when that statement is executed", because, for example: def foo() { new { val a: Any = sys.error("b is " + b) val b: Any = sys.error("a is " + a) } } This gives "b is null" . b is never evaluated and its error is never thrown. But it is in scope as soon as control enters the block. Yes, but there is one nice trick: if you have lazy value, and during first time evaluation it will

Wicket has this device called a lazy proxy factory. Given: <property name="foo" ref="beanx"/> the idea is to auto-generate a proxy in place of 'beanx', and then only initialize beanx if and when something actually calls a method on it. It seems as if this might be a core Spring capability. Is it there somewhere? See LazyInitTargetSource ; that might do what you want. It requires use of lazy-init="true" on the target bean as well, though. Spring singleton beans, the closest thing to what you want, are created when the spring context is initialized: http://static.springsource.org/spring/docs/2.0