Getting exception in thread “main” java.lang.StackOverflowError

Question

I am new to Java and OOPs and here is my issue. When I run the below code, I get the

Exception in thread \"main\" java.lang.StackOverflowError.

Answer 1

Your class JavaApplication1 has member JavaApplication1 ja initialized in-place. This means that when you create new instance of JavaApplication1 in main() method you call implicit default constructor that calls new JavaApplication1() again, and again, and again.

If your want your code to work, first remove line

JavaApplication1 ja =new JavaApplication1();

Answer 2

I think you end up creating JavaApplication1 objects all the time which cause the stackOverflow exception. You should remove the line with the comment.

 App2 a2 = new App2();
 JavaApplication1 ja =new JavaApplication1(); //why do you need this?
 public void run(){

Answer 3

Your class JavaApplication1 has field JavaApplication1 ja which holds another instance of JavaApplication1 class, which also has its own ja field which holds another instance of JavaApplication1, and so on and on.

In other words, when you create instance of JavaApplication1 this instance creates its inner instance of JavaApplication1 and this inner instance creates another JavaApplication1 instance, which again creates instance JavaApplication1... until stack will be full.

So when you run this code in your main method

JavaApplication1 ja1 = new JavaApplication1();

something like this happens

       +-----------------------------------------------+
ja1 -> | JavaApplication1 instance                     |
       +-----------------------------------------------+
       |                                               |
       |       +------------------------------------+  |
       | ja -> | JavaApplication1 instance          |  |
       |       +------------------------------------+  |
       |       |                                    |  |
       |       |       +-------------------------+  |  |
       |       | ja -> |JavaApplication1 instance|  |  |
       |       |       +-------------------------|  |  |
       |       |       |                         |  |  |
       |       |       | ja -> ....              |  |  |
       |       |       +-------------------------+  |  |
       |       +------------------------------------+  |
       +-----------------------------------------------+

Anyway I don't see where ja field is ever used, so consider removing it from your code.

Answer 4

The problem is that you can't do something like this:

Class Try{
Try try = new Try();
public static void main(String[] arg)
{
Try try1 = new Try();
}

The issue with above code is that first the execution will start with your main method(ofcourse in this particular case :) ) then the try1 object will get created and all of the Class fields will get initialized, since you created an object of the same class you are in as a Class Field() it will try to re-initialize the Class fields, ending up in an infinite loop and inevitably the Famous STACK OVERFLOW error!

Now, talking in context of your question:

App2 a2 = new App2();
JavaApplication1 ja =new JavaApplication1(); //remove this line, it is causing the SO-error!!!