About StackOverFlow problem

[kevin saber]

Please look at two following codes：

 public class MyApp {
	MyApp  t = new MyApp();

	public static void main(String[] args) {
		new MyApp();
	}
}   

and

 public class MyApp {
	static MyApp  t = new MyApp();

	public static void main(String[] args) {
		new MyApp();
	}
}   

Can somebody tell me how each code run and how one of them lead to stackoverflow error ？

[Raj Kamal]

Hi,

In the first code there is an instance variable 't' of the same type. This leads to a cyclic creation of objects, hence the StackOverFlow. Whereas in the second the 'static' modifier makes the property at the class level i.e. There is only one reference which is shared by all objects of the class and hence there is no repetitive object creation. So a StackOverFlow does not arise with this case. Hope I am clear enough with my explanation?

Cheers,
Raj.

[Brij Garg]

public class MyApp {
MyApp t = new MyApp();

public static void main(String[] args) {
//statement1// new MyApp();
}
}

Above given code should give StackOverFlow.
every MyApp object has an instance variable t which is refering to another MyApp object.

When this class will execute then statement at line 1 will execute and it leads to the creation of never ending MyApp objects until StackOverFlow.

[Harpreet Singh janda]

Because in first case you are recursively creating an object of MyApp class. Line #2

    MyApp  t = new MyApp();    

Whenever you will create a new object of MyApp class it will execute the line # 2 and again will create another instance of MyApp and again and again till the memory will not be flooded with MyApp objects,

But in second case it will not happen because here you have declared the MyApp object as static and there will be only one object for this class member (MyApp at line 2). A new object will be created only once the class will be loaded first time so no recursive call which could lead to StackOverflowError.

[kevin saber]

still a little abstract...
But i will remember it .

[Lorand Komaromi]

kevin saber wrote:But i will remember it .

You don't need to remember the exact explanation, you just need to understand the basics, e.g. how class members are initialized and that endless (or long enough) recursion causes StackOverFlow...

[Jesper de Jong]

kevin saber wrote:still a little abstract...

Well, let's look at what happens exactly when you run your first code example.

1. Line 5: you create a new MyApp() object.
2. As part of the initialisation of that new object, line 2 is run.
3. Line 2: you create a new MyApp() object.
4. As part of the initialisation of that new object, line 2 is run.
5. Line 2: you create a new MyApp() object.
6. As part of the initialisation of that new object, line 2 is run.
7. Line 2: you create a new MyApp() object.
8. As part of the initialisation of that new object, line 2 is run.
9. ...

10000000. There is no memory available on the stack anymore and you get a StackOverflowError.

You are trying to create a MyApp object, which contains a MyApp object, which also contains a MyApp object, ...

You have an infinite recursive loop.