Object initialization in Java

Question

Consider following code.

public class Skyler {
Skyler s1=new Skyler();
public static void main(String asd[]){
         Skyler s2=new Skyler();
    }
}

It generates java.lang.StackOverflowError Exception. Why?

Consider following code also.

public class Skyler {
    Skyler s1=new Skyler();
    static Skyler s2=new Skyler();
    Skyler(){
        System.out.println("const");
    }
    public static void main(String sdp[]){}
}

This is also generating same java.lang.StackOverflowError exception. Why?

Is reason same for both Exceptions?

Suresh Atta · Accepted Answer · 2015-10-09 11:36:15Z

3

You are undergone a loop where the constructor calling it self for servaral times until it's overflowed.

For ex :

And the reason is same in both cases. It's calling it self endlessly.

In your both cases there is only once difference that you provided a default no org constructor with a print statement so that you can see that print statement until you got the error.

edited Oct 9, 2015 at 11:36

answered Oct 9, 2015 at 11:30

Suresh Atta

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2 Comments

prateek tomar Over a year ago

How come is it an ERROR ? Is it not an Exception?

Suresh Atta Over a year ago

@prateektomar No. There is a difference between error and exception.

Eran · Accepted Answer · 2015-10-09 11:23:46Z

2

Each time you create an instance of Skyler, the s1 member of that instance is initialized, which creates another instance of Skyler, which initializes the s1 member of that other instance, which creates another instance of Skyler and so on...

In other words, you have an infinite chain of calls to the Skyler constructor, which causes StackOverflowErr.

answered Oct 9, 2015 at 11:23

Eran

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3 Comments

prateek tomar Over a year ago

Is reason same for exceptions in both the code snippets?

Suresh Atta Over a year ago

@prateektomar Yes. It is. Added that in my answer. Please read.

Eran Over a year ago

@prateektomar Yes. The only difference between the two snippets is where the first instance of Skyler is created (in the main method in the first snippet and in the initialization of a static variable in the second snippet). Once that takes place, the initialization Skyler s1=new Skyler(); causes the infinite constructor calls leading to the exception.

starkshang · Accepted Answer · 2015-10-09 11:23:07Z

1

Delete Skyler s1=new Skyler();.With your code,Skyler class has a variable whose type is Skyler,then it will be create a Skyler again and again,so StackOverflowException exists.

answered Oct 9, 2015 at 11:23

starkshang

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Comments

SomeJavaGuy · Accepted Answer · 2015-10-09 11:24:08Z

1

Check the logic, you create a new Skyler, what does this do? It creates a new Skyler, surprisingly this new Skyler creates another new Skyler. This all comes from your line Skyler s1=new Skyler();(the one that is not static), which recursivly creates endles instances of the Object Skyler.

answered Oct 9, 2015 at 11:24

SomeJavaGuy

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Comments

Marco · Accepted Answer · 2015-10-09 11:24:13Z

1

The class Skyler calls its own constructor. So while creating an instance of Skyler, another instance of Skyler is created and so on... the result is a StackOverflow.

answered Oct 9, 2015 at 11:24

Marco

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