1 import java.util.EnumSet;
 2
 3
 4 public class Client {
 5     public static void main(String[] args) {
 6         //创建生成包含所有枚举项的EnumSet
 7         EnumSet<Const> cs = EnumSet.allOf(Const.class);
 8         EnumSet<LargeConst> lcs = EnumSet.allOf(LargeConst.class);
 9         //打印出枚举项数量
10         System.out.println("Const枚举项数量：" + cs.size());
11         System.out.println("LargeConst枚举项数量：" + lcs.size());
12         //输出两个EnumSet的class
13         System.out.println(cs.getClass());
14         System.out.println(lcs.getClass());
15     }
16 }
17
18 //普通枚举项，数量小于64
19 enum Const {
20     A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, AA, BA, CA, DA, EA, FA, GA, HA, NA, OA, PA, QA, RA, SA, TA, UA, VA, WA, XA, YA, ZA, BC, CC, DC, EC, FC, GC, HC, IC, JC, KC, LC, MC, NC, OC, PC, QC, RC;
21 }
22 //大枚举，数量超过64
23 enum LargeConst {
24     A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, AA, BA, CA, DA, EA, FA, GA, HA, IA, JA, KA, LA, MA, NA, OA, PA, QA, RA, SA, TA, UA, VA, WA, XA, YA, ZA, AB, BB, CB, DB, EB, FB, GB, HB, IB, JB, KB, LB, MB;
25 }

Const枚举项数量：64
LargeConst枚举项数量：65
class java.util.RegularEnumSet
class java.util.JumboEnumSet

 1     /**
 2      * Creates an enum set containing all of the elements in the specified
 3      * element type.
 4      *
 5      * @param elementType the class object of the element type for this enum
 6      *     set
 7      * @throws NullPointerException if <tt>elementType</tt> is null
 8      */
 9     public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> elementType) {
10         EnumSet<E> result = noneOf(elementType);//生成一个空的EnumSet
11         result.addAll();..加入所有的枚举项
12         return result;
13     }

 1     /**
 2      * Creates an empty enum set with the specified element type.
 3      *
 4      * @param elementType the class object of the element type for this enum
 5      *     set
 6      * @throws NullPointerException if <tt>elementType</tt> is null
 7      */
 8     public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType) {
 9         Enum[] universe = getUniverse(elementType);
10         if (universe == null)
11             throw new ClassCastException(elementType + " not an enum");
12
13         if (universe.length <= 64) //枚举数量小于64
14             return new RegularEnumSet<>(elementType, universe);
15         else //枚举数量大于64
16             return new JumboEnumSet<>(elementType, universe);
17     }

 1 class RegularEnumSet<E extends Enum<E>> extends EnumSet<E> {
 2     private long elements = 0L;//记录所有枚举排序号,注意是long型
 3     RegularEnumSet(Class<E>elementType, Enum[] universe) {//构造函数
 4         super(elementType, universe);
 5     }
 6     void addAll() {//加入所有元素
 7         if (universe.length != 0)
 8             elements = -1L >>> -universe.length;
 9     }
10 }    

class JumboEnumSet<E extends Enum<E>> extends EnumSet<E> {private long elements[];//映射所有的枚举项JumboEnumSet(Class<E>elementType, Enum[] universe) {//构造函数super(elementType, universe);elements = new long[(universe.length + 63) >>> 6];//默认长度是枚举项数量除以64再加1
    }void addAll() {//elements中每个元素表示64个枚举项for (int i = 0; i < elements.length; i++)elements[i] = -1;elements[elements.length - 1] >>>= -universe.length;size = universe.length;}
}