public class Country { int population; double area; String name; @Override public int hashCode() { return 0; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Country other = (Country) obj; if (Double.doubleToLongBits(area) != Double .doubleToLongBits(other.area)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; if (population != other.population) return false; return true; } }