Plant.java

package effectivejava.chapter6.item37;
import java.util.*;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toSet;

// Using an EnumMap to associate data with an enum (Pages 171-3)

// Simplistic class representing a plant (Page 171)
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 String toString() {
        return name;
    }

    public static void main(String[] args) {
        Plant[] garden = {
            new Plant("Basil",    LifeCycle.ANNUAL),
            new Plant("Carroway", LifeCycle.BIENNIAL),
            new Plant("Dill",     LifeCycle.ANNUAL),
            new Plant("Lavendar", LifeCycle.PERENNIAL),
            new Plant("Parsley",  LifeCycle.BIENNIAL),
            new Plant("Rosemary", LifeCycle.PERENNIAL)
        };

        // Using ordinal() to index into an array - DON'T DO THIS!  (Page 171)
        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);
        // Print the results
        for (int i = 0; i < plantsByLifeCycleArr.length; i++) {
            System.out.printf("%s: %s%n",
                    Plant.LifeCycle.values()[i], plantsByLifeCycleArr[i]);
        }

        // Using an EnumMap to associate data with an enum (Page 172)
        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);

        // Naive stream-based approach - unlikely to produce an EnumMap!  (Page 172)
        System.out.println(Arrays.stream(garden)
                .collect(groupingBy(p -> p.lifeCycle)));

        // Using a stream and an EnumMap to associate data with an enum (Page 173)
        System.out.println(Arrays.stream(garden)
                .collect(groupingBy(p -> p.lifeCycle,
                        () -> new EnumMap<>(LifeCycle.class), toSet())));
    }
}