public class Country {String name;long population;public Country(String name, long population) {super();this.name = name;this.population = population;}public String getName() {return name;}public void setName(String name) {this.name = name;}public long getPopulation() {return population;}public void setPopulation(long population) {this.population = population;}// If length of name in country object is even then return 31(any random// number) and if odd then return 95(any random number).// This is not a good practice to generate hashcode as below method but I am// doing so to give better and easy understanding of hashmap.
    @Overridepublic int hashCode() {if (this.name.length() % 2 == 0)return 31;elsereturn 95;}@Overridepublic boolean equals(Object obj) {Country other = (Country) obj;if (name.equalsIgnoreCase((other.name)))return true;return false;}}

public class HashMapStructure {public static void main(String[] args) {Country india = new Country("India", 1000);Country japan = new Country("Japan", 10000);Country france = new Country("France", 2000);Country russia = new Country("Russia", 20000);HashMap<Country, String> countryCapitalMap = new HashMap<Country, String>();countryCapitalMap.put(india, "Delhi");countryCapitalMap.put(japan, "Tokyo");countryCapitalMap.put(france, "Paris");countryCapitalMap.put(russia, "Moscow");Iterator<Country> countryCapitalIter = countryCapitalMap.keySet().iterator();// put debug point at this linewhile (countryCapitalIter.hasNext()) {Country countryObj = countryCapitalIter.next();String capital = countryCapitalMap.get(countryObj);System.out.println(countryObj.getName() + "----" + capital);}}}

static class Entry implements Map.Entry{final K key;V value;Entry next;final int hash;...//More code goes here
}