java - stackoverflow error when creating object outside the main method

Question

While running this code it shows Stackoverflow error. What is it I am doing wrong, why does the code compile?

public class Foo {
    int a = 5;
    Foo f = new Foo();

    void go() {
        System.out.println(f.a);
    }

    public static void main(String[] args) {
        Foo f2 = new Foo();
        f2.go();
    }
}

Answer 1

Foo f=new Foo();

You create an instance of Foo, with a variable which itself is an instance of Foo, and initialize it in the constructor.

This causes infinite recursion of constructor invokations, untill your stack is out of space.