Thread: recursion on initialization

i am trying to make a game, for some reason i have begun to get a java.lang.StackOverflowError.
im not exactly sure how i can fix it. only removing line 14 from infopannel1 (and everything that used that class.) seems to work. im not sure what else i can do to fix it. or why its resulting in stack overflow for that matter.
i am putting in a link for the files i wrote this using bluej
(several classes have no relevance, errorv2, demonstration, folderreadertest, ReadWithScanner, saveloadtest, menutest,rannum, and menutestTester. are all irrelivent to my problem.)
https://www.dropbox.com/sh/7f2u492aeitdrq0/Mt9BfNOcEK

java.lang.StackOverflowError
at failsafe.<init>(failsafe.java:9) ---> public class failsafe
at mainmenu.<init>(mainmenu.java:16) -----> failsafe choice = new failsafe();
at infopannel1.<init>(infopannel1.java:14)-----> mainmenu MM = new mainmenu();
at mainmenu.<init>(mainmenu.java:18)-----> infopannel1 info1 = new infopannel1();
at infopannel1.<init>(infopannel1.java:14)-----> mainmenu MM = new mainmenu();
that is the code at each line. after that it goes from mainmenu.java:18 and infopannel1.java:14.

im sorry, i dont quite understand.. the same style of loop as those two classes call appears several times without any such problem
could you give me an example?

i separated them by class
i gave a link to the folder, opened in blujay it contains all of them.
do you want me to put the entirety of the involved classes in?

I can't quite make sense of the code posted in post #17, so I took the liberty of taking a peek at mainmenu.java and infopannel1.java in Dropbox based on the stack trace mentioned in post #3. The line numbers are slightly different from those in the stack trace, but I think I see the problem.

In mainmenu.java:

public class mainmenu
{
    ...
    printer print = new printer();
    infopannel1 info1 = new infopannel1();
    ...

In infopannel.java:

public class infopannel1
{
    ...
    failsafe choice = new failsafe();
    mainmenu MM = new mainmenu();
    ...

The instance variable initialiser in each of the classes instantiates the other class. In the above case, during the instantiation of the mainmenu class, the instance variable initialiser, infopannel1 info1 = new infopannel1(), is executed. This results in the instantiation of the infopannel1 class, where the mainmenu MM = new mainmenu() instance variable initialiser is executed. Ad infinitum.

To clarify this point, consider the example program below, which exhibit the same StackOverFlow error problem:

public class InitRecursion {
    public static void main(String[] args) {
        ClassOne c1 = new ClassOne();
        System.out.println("Done");
    }
}
 
class ClassOne {
    private ClassTwo two = new ClassTwo();
}
 
class ClassTwo {
    private ClassOne one = new ClassOne();
}

If you run the above program, you'd get a StackOverFlowError with a very long stack trace.

Note that when a class is instantiated, the new object is initialised by going through the following procedure (on a high-level):

1. invoke another constructor in the same class (if such a call exists)
2. invoke a superclass constructor
3. execute instance initialisers and instance variable initialisers
4. execute the rest of the body of the constructor

(See Object initialization in Java | JavaWorld and Chapter*12.*Execution for elaboration on the above.)

The above procedure is what <init> in "mainmenu.<init>" and "infopannel1.<init>" in the stack trace refer to. In your case, procedure #3 is what you're concerned with. infopannel1 info1 = new infopannel1() and mainmenu MM = new mainmenu() are the instance variable initialisers that are executed during object initialisation, and they are the source of the recursive calls that led to the StackOverFlowError.

Quite advanced stuff, but the bottom line is don't instantiate each other in the instance variable declarations (nor in the constructors).

just to make sure i understand, which i believe i do, basically every time something such as

class ClassOne {
    private ClassTwo two = new ClassTwo();
}

is typed, it creates an instance of ClassTwo, for the use of class ClassOne.
thus what ive done is created two instances which infinitely call upon eachother. thus stack overflow.