Exception in thread "main" java.lang.StackOverflowError

[rohit-kumar Kumar]

class P
{


P p1=new P();
protected P printInfo()
{

System.out.println("Inside class p method");

return p1;

}

}

class Q extends P
{

Q q1=new Q();


public Q printInfo()
{

System.out.println("Inside class q method");
return q1;

}


}

public class override{



public static void main(String[] arg)
{

P p=new P();
Q q=new Q();
P r=new Q();

p=p.printInfo();
q=q.printInfo() ;
r=r.printInfo() ;

}


}


anyone please explain the error.

[Christophe Verré]

In the Q class, having Q q1=new Q(); is probably not a good idea. This will cause to instanciate Q objects forever. Well, until StackOverflowError is thrown.

[rohit-kumar Kumar]

thankx for the reply.

but what about the P class?

Explain in full detail.

Thanks in advance.

[Jesper de Jong]

Welcome to JavaRanch. Please UseCodeTags when you post source code.

Do you understand what happens if you have code like this:

class P {
	P p1 = new P();
	
	// ...
}

(you have exactly the same construct in class Q).

What happens when you create a new P object?

1. A new P object is created.
2. The object is initialized. It has a member variable p1, for which a new P object needs to be created.
3. That new P object is created.
4. But it also needs to be initialized. It has its own member variable p1, for which a new P object needs to be created.
5. Go to step 3.

So, there is an infinite recursive loop which keeps running until the stack overflows, and then you get a StackOverflowError.

[Rob Spoor]

First of all, UseCodeTags. You can edit your post to add them.

Like Q, class P has an instance field of type P itself that is initialized to a new P object whenever a new P object is created. That means that when you create one P object, you get the following chain of calls:

- new P()
  - new P()
    - new P()
      - new P()
        - new P()
...

This ends by the JVM throwing a StackOverflowError.

[rohit-kumar Kumar]

Thanks a lot.

[Rob Spoor]

You're welcome.