Test17_HM_B

import java.util.HashMap;

public class Test17_HM_B {
    public static void main(String[] args) {
        final HashMap<Object,Object> hashMapOne = new HashMap<>();

        hashMapOne.put(1, hashMapOne);

        System.out.println("Size    :"+hashMapOne.size());
        System.out.println("Elements : "+hashMapOne.toString());
        System.out.println();

        final HashMap<Object,Object> hashMapTwo = new HashMap<>();

        hashMapTwo.put(2, hashMapTwo);

        System.out.println("Size    :"+hashMapTwo.size());
        System.out.println("Elements : "+hashMapTwo.toString());
        System.out.println();

        hashMapTwo.put(1, hashMapOne);
        hashMapOne.put(2, hashMapTwo);

        System.out.println("Size    :"+hashMapOne.size());
        System.out.println("Elements : "+hashMapOne.toString());    // It "blows up" here.
        System.out.println();
        System.out.println("Size    :"+hashMapTwo.size());
        System.out.println("Elements : "+hashMapTwo.toString());
        System.out.println();
    }
}