class Plant {
	enum LifeCycle { ANNUAL, PERENNIAL, BIENNIAL }
	
	final String name;
	final LifeCycle lifeCycle;

	Plant(String name, LifeCycle lifeCycle) {
		this.name = name;
		this.lifeCycle = lifeCycle;
	}

	@Override public Sring toString() {
		return name;
	}
}

Set<Plant>[] plantsByLifeCycleArr =
        (Set<Plant>[]) new Set[Plant.LifeCycle.values().length];
for (int i = 0; i < plantsByLifeCycleArr.length; i++)
    plantsByLifeCycleArr[i] = new HashSet<>();
for (Plant p : garden)
    plantsByLifeCycleArr[p.lifeCycle.ordinal()].add(p);
// 결과 출력
for (int i = 0; i < plantsByLifeCycleArr.length; i++) {
    System.out.printf("%s: %s%n",
            Plant.LifeCycle.values()[i], plantsByLifeCycleArr[i]);

// 코드 37-2 EnumMap을 사용해 데이터와 열거 타입을 매핑한다. (227쪽)
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);
System.out.println(plantsByLifeCycle);

System.out.println(Arrays.stream(garden)
				.collect(groupingBy(p -> p.lifeCycle)));

Arrays.stream(garden)
		.collect(groupingBy(p -> p.lifeCycle,
			() -> new EnumMap<>(LifeCycle.class), toSet())));