Java中EnumMap代替序数索引代码详解

public class Herb {
  public enum Type { ANNUAL, PERENNIAL, BIENNIAL };
  private final String name;
  private final Type type;

  Herb(String name, Type type) {
    this.name = name;
    this.type = type;
  }

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

//Using ordinal() to index an array - DON'T DO THIS
Herb[] garden = ... ;

//Indexed by Herb.Type.ordinal()
Set<Herb>[] herbsByType = (Set<Herb>[])new Set[Herb.Type.values().length]; 
for(int i=0; i<herbsByType.length; i++) {
  herbsByType[i] = new HashSet<Herb>();
}

for(Herb h : garden) {
  herbsByType[h.type.ordinal()].add(h);
}

//Print the results
for(int i=0; i<herbsByType.length; i++) {
  System.out.printf("%s: %s%n", Herb.Type.values()[i], herbsByType[i]);
}

//Using an EnumMap to associate data with an enum
Map<Herb.Type, Set<Herb>> herbsByType = new EnumMap<Herb.Type, 
Set<Herb>>(Herb.Type.class);

for(Herb.Type t : Herb.Type.values)
  herbsByType.put(t, new HashSet<Herb>());

for(Herb h : garden)
  herbsByType.get(h.type).add(h);

System.out.println(herbsByType);