[Effective Java 3/e] 아이템 37 - odinal 인덱싱 대신 EnumMap을 사용하라

Set<Plant>[] plantsByLifeCycle = (Set<Plant>[]) new Set[Plant.LifeCycle.values().length];

for(int i = 0; i < plantsByLifeCycle.length; i++)
  plantsByLifeCycle[i] = new HashSet<>();

for(Plant p : garden)
  plantsByLifeCycle[p.lifeCycle.ordinal()].add(p);
}

Map<Plant.LifeCycle, Set<Plant>> plantsByLifeCycle = new EnumMap<>(Plant.LifeCycle.class);

for(Plant.LifeCycle lc : Plant.LifeCycle.values())
  plantsByLifeCycle.put(lc, new HashSet<>());

for(Plant p : garden)
  plantsByLifeCycle.get(p.lifeCycle).add(p);
}