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This is my code :

public class ConstructorsDemo{

    public static void main(String a[]){

        Cons1 c1 = new Cons1();

    }

}

class Cons1{

    Cons1 c = new Cons1();// the error is in this line

    Cons1(){

        //does somwthing

    }
}

So I get an infinite loop error here (Stackoverflow). However it's fine if I comment out any of the two objects I have created.

How is the object c in my code causing Stackoverflow error?

Nisse Engström
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Anuraag
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4 Answers4

2

Lets have a look at your class.

It has an (empty) constructor, and a field of the same type as the class.

And that field is initialized directly in place.

Thing is: there is a well-defined process in Java that dictates how/when constructors are called, and how fields of a class are initialized. And well, member fields are initialized as part of calls to "new".

Leading to: when "new" is called in your main class, a new Cons1 object should be created and initialized. That Cons1 object has that Cons1 field. Which requires a new Cons1 object to be initialized with ... and so on.

And that is how you created your first never-ending recursion in Java.

GhostCat
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Cons1 c = new Cons1();//

Please remove this statement and initialize it wherever you are going to use it . Code is recursive .

Deepak
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First point: this is infinite recursion, not an infinite loop. There's a big difference. There are perfectly legitimate reasons to use infinite loops and they will not, in general, cause stack overflow exceptions. However, there are no legitimate use cases for infinite recursion and its use will invariably lead to a stack overflow exception. (I suppose you could maybe argue for infinite tail recursion in a few odd situations for languages that have that but still...) If you get a stack overflow exception, it's almost certainly infinite recursion rather than an infinite loop.

The basic problem here, as others have pointed out, is that every time you call "new" it, in turn, creates a new object, which in turn creates a new object, and so on and so forth.

Cons1 c = new Cons1();
EJoshuaS - Stand with Ukraine
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you're creating the object recursively,each time you create the object this is why you got the infinite loop and witch causes the stack overflow

whyn0t
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    Infinite recursion, *not* an infinite loop. Infinite loops don't usually cause stack overflow exceptions. – EJoshuaS - Stand with Ukraine Aug 16 '16 at 04:40
  • recursion has the same loop concept since it is a call repetition, until the return condition is meet. Whenever the method is invoked, a new block is created in the stack memory for the method to hold local primitive values and reference to other objects in the method and this is what caused the stack overflow – whyn0t Aug 16 '16 at 15:50
  • Yes but an infinite loop doesn't grow the stack in the same way because once you return from a function call you can shrink the stack again and any local variables become eligible for garbage collection (at least in a managed language like Java or C#). This isn't the case in the code he put above. if you do while (true) { someMethodCall(a, b, c); } the stack will grow to accommodate someMethodCall and then immediately shrink again once someMethodCall returns but if you do someMethodCall(a, b, c) { return someMethodCall(a, b, c); } you'll just keep growing the stack indefinitely. – EJoshuaS - Stand with Ukraine Aug 16 '16 at 16:13