java.lang.StackOverflowError while calling a method

Question

I am learning interface behavior. i have created a interface and its implementer class, while calling method m1() i got java.lang.StackOverflowError. i dont know why. can anybody tell me proper reason behind this !!!!!! Here is the code :

public interface Employee {
     String name="Kavi Temre";
}

public class Kavi implements Employee{
    Employee e= new Kavi();
    public static void main(String[] args) {

        Kavi kt=new Kavi();
        kt.m1();
    }

    void m1()
    {
        System.out.println(Employee.name);
        //System.out.println(e.name);
    }
}

both sysout give the same error : please tell me what is actually going on here ??

Console output:

Exception in thread "main" java.lang.StackOverflowError
    at Kavi.<init>(Kavi.java:2)
    at Kavi.<init>(Kavi.java:2)
    at Kavi.<init>(Kavi.java:2)
    at Kavi.<init>(Kavi.java:2)
    at Kavi.<init>(Kavi.java:2)
    at Kavi.<init>(Kavi.java:2)
    at Kavi.<init>(Kavi.java:2)
    .....

Answer 1

When you call

Kavi kt=new Kavi();

it initializes the e member :

Employee e = new Kavi();

which then initializes its own e member, which gives you an infinite chain of calls to the Kavi constructor. Hence the StackOverflowError.

It's equivalent to :

Employee e;
public Kavi ()
{
    e = new Kavi();
}

A constructor shouldn't call itself in an infinite loop.

Removing the Employee e = new Kavi() line will solve your issue. If your class must hold a reference to an Employee , consider passing it to the constructor :

public Kavi ()
{
    this.e = null;
}

public Kavi (Employee e)
{
    this.e = e;
}

public static void main(String[] args) {

    Employee e = new Kavi ();
    Kavi kt=new Kavi(e);
    ...
}

An alternative solution is to change :

Employee e = new Kavi();

to

static Employee e = new Kavi();

That would be a valid solution if all instances of Kavi share the same Employee instance referred by e .

Answer 2

Inside your class Kavi you are declaring a field e of type Employee and initialize it with a new Kavi object.

When creating the first instance of the class Kavi you are triggering the aforementioned initialization and create a new Kavi object (line 2) that also creates a new Kavi and so on and so on. So the problematic line is

Employee e= new Kavi();

After a good number of Kavi objects have been created, the stack will reach its limit and the exception will be thrown.