Static Variables - Im on WinXP and LinuxMint, on Linux i have no problems ??

Newbie & Debugging Questions
#1

Hello!

I have an boardgames site on a build.

I have all my game classes ( currently 4 games ) in one applet.

My problem comes when i restart my games, on WinXP my Applet wont work fully after i double choose a game, there is problems on variable updating ??

All my variables are on a static “style”.

In what ways the Linux and Windows static variables differ, im with Sun Java 1.6.0.20.

Thanks…

#2

Never use non-final static variables in applets.

Multiple applets launch in the same VM (unless explicitly instructed not to), so all your applets share the same static variables. Even leaving a page and loading a brand new applet will launch your applet in the VM of the discarded applet, unless some timeout occurred, or you cleared your classloader cache (java console -> type XC).

#3

First only Java decides how static variables are handled (not Windows or Linux). However as Riven pointed out Applets are typically re-used on Windows, but not on LinuxMint, and so you are missing out on what is known as “static initialization”. That is where the static aspect of a class is initialized for the first time; which doesn’t occur if the applet is simply being re-used (as this is more efficient then making a new applet each time). I’d personally suspect skipping this is down to how the browser is handling the JVM, not the OS.

As a quick fix you can manually initialize all of your non-final static variables in the Applet’s start method (maybe in init too, but I’m not sure if this will only be called once when it is created).

#4

Bad idea; 2 instances of said applet running concurrently will be sharing the same static variables.
That leaves the door wide open to a world of painful-to-find bugs.

Even using statics in an application can cause problems.

Use them in an application -> fine.
Application code gets refactored into a library for reuse -> fine.
Library gets used by an Applet -> oh dear.

Best advice is to not use static variables. Ever.

#5

StaticVariables!

I have now removed all, i think, static variables from my code, thank you for pointing me my bug, i only had 4 game demoes to track down,
i will later on build atleast 30 AWT games to my site.

Im only a hobbyer with Java, i have no school history on computers.

so, i removed all static variables and changed my code to following style.

My chessgame for example holds 5 classes.

ChessGame.java,
ChessGame_Variables.java,
ChessGame_Init.java,
ChessGame_GameLogic.java,
ChessGame_ScreenUpdate.java.

My variables are all on ChessGame_Variables.java file.

I call it as following ->

at ChessGame.java i have

public ChessGame_Variables vars = new ChessGame_Variables ();

and at other classes _Init, _GameLogic, _ScreenUpdate i have an contrucstors for vars,


public ChessGame_Variables vars = null;

public ChessGame_XXXXX ( ChessGame_Variables fvars )
{					
    vars = fvars;
}

I hope i get it right this time ;), i will work like this way on my futher releases too !!
It was a bit of a dump idea from me to try to build my Applets with static variables !!

Thanks…

#6

I’m surprised they don’t load them using seperate class loaders.

#7

simple fix, add the following parameter in your applet tag and it’ll load it in a new classloader as opposed to sharing one.

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