Method static variables

Why aren't there static variables in methods in Java like there are in C++? Is that against OO design?
LVL 7
Sasha_MapaAsked:
Who is Participating?
 
heyhey_Connect With a Mentor Commented:
in C (forget C++) you have functions & static variables to keep some state between function calls.

in Java you have Objects with methods and fields which keep the object state between method calls :)
0
 
Laminamia063099Commented:
C++ static variables are against good design in general.  In C++ they are used to track changes or values from one method call to the next.  This is bad design because the same call to the method with the same parameters and same class variable values can have different results because a static method variable has different values.

In good program design, the same call to a class method with the same parameters and the same instance values should always produce the same result.  C++ static method variables break this design constraint and code becomes unpredictable.

Laminamia :)
0
 
Sasha_MapaAuthor Commented:
Ok, I see.
Here is a simplification of the case when the need for a method static variable arised:
I wanted to get lots of images, add them to a media tracker and then wait for them to load. I didn't want to repeat the same code of

myImage46 = getImage(getCodeBase(),"imagename.gif");
imageTracker.addImage(myImage,46);

many times so I wrote a method that would take the name of the image and the MediaTracker as arguments and would return the Image having added it to the MediaTracker. The problem is that I don't know the number of the image from within that method, and a static variable (a static variable in that method) which would increase by 1 every time the method would be called seemed the right way to go here. Not being able to use that I had to add a private instance variable to my applet. So I ended up adding an instance variable which did not represent any actual state of my applet. That sounds like bad OO design too...no?
0
Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

 
heyhey_Commented:
if method that loads images is part of your applet, than the information about how many images are loaded is part of that applet too :)

if you put this method in some specila ImageManager object (which can be implemented as Singleton), this field will be member of that object.

there is no such thing as 'method with state' - only object have state.

(in C you have functions with state)
0
 
Sasha_MapaAuthor Commented:
LOL, I see what you mean now...
What's a Singleton? A static object shared between all applications?
0
 
Laminamia063099Commented:
A Singleton object only is instantiated once.  It does this by controlling it's creation.  This is important because anyone who has a handle to the singleton object has a handle to the same object.  You have to make the constructor private/protected and provide a method that returns a handle to the instance:

class Singleton {
  protected static handleToInstance = null;
  protected Singleton(){}
  public getInstance (){
     if (handleToInstance == null)
          handleToInstance = new Singleton();
     return handleToInstance;
  }
}

It's great when used in appropriate areas, like heyhey's suggestion.

Laminamia
0
 
Sasha_MapaAuthor Commented:
Cool! I'll see whether it fits somewhere in my app. Thanks a lot guys.
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.