Why does StackOverflowError occur in the below scenario?

Question

public class B {

    public static void main(String[] args) {
        A a = new A();
    }
}

public class A {

    A b = new A();
}

Answer 1

Because every A creates an inner field named b of type A. That's infinitely recurisve, because to create a b you must also create an A (which adds another b). Because initializers are copied to the default constructor, your example is equivalent to something like,

public class A {
   // A b=new A(); 
   A b;
   public A() {
       super();
       b = new A();
   }
}