EnumSet
EnumSet是Java枚举类型的泛型容器，Java既然有了SortedSet、TreeSet、HashSet等容器，为何还要多一个EnumSet<T>呢？答案肯定是EnumSet有一定的特性，举个例子，EnumSet的速度很快。其他特性就不一一列举了，毕竟本文的内容不是介绍EnumSet的特性。
专门为枚举类设计的集合类，所有元素必须是枚举类型
EnumSet的集合元素是有序的，内部以位向量的形成存储，因此占用内存小，效率高
不允许加入null元素
源码
package java.util;import sun.misc.SharedSecrets;public abstract class EnumSet<E extends Enum<E>> extends AbstractSet<E> implements Cloneable, java.io.Serializable{ /** * 元素类型 */ final Class<E> elementType; /** * 通过数组存储元素 */ final Enum[] universe; private static Enum[] ZERO_LENGTH_ENUM_ARRAY = new Enum[0]; EnumSet(Class<E>elementType, Enum[] universe) { this.elementType = elementType; this.universe = universe; } /** * 创造一个空的 enum set 并制定其元素类型 * @param elementType the class object of the element type for this enum * set * @throws NullPointerException if <tt>elementType</tt> is null */ public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType) { Enum[] universe = getUniverse(elementType); if (universe == null) throw new ClassCastException(elementType + " not an enum"); if (universe.length <= 64) return new RegularEnumSet<>(elementType, universe); else return new JumboEnumSet<>(elementType, universe); } /** * 创建一个包含所有在指定元素类型的元素的枚举set * * @param elementType the class object of the element type for this enum * set * @throws NullPointerException if <tt>elementType</tt> is null */ public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> elementType) { EnumSet<E> result = noneOf(elementType); result.addAll(); return result; } /** * Adds all of the elements from the appropriate enum type to this enum * set, which is empty prior to the call. */ abstract void addAll(); /** * 创建一个枚举设置相同的元素类型与指定枚举set * * @param s the enum set from which to initialize this enum set * @throws NullPointerException if <tt>s</tt> is null */ public static <E extends Enum<E>> EnumSet<E> copyOf(EnumSet<E> s) { return s.clone(); } /** * 创建一个枚举集从指定集合初始化，最初包含相同的元素 * @param c the collection from which to initialize this enum set * @throws IllegalArgumentException if <tt>c</tt> is not an * <tt>EnumSet</tt> instance and contains no elements * @throws NullPointerException if <tt>c</tt> is null */ public static <E extends Enum<E>> EnumSet<E> copyOf(Collection<E> c) { if (c instanceof EnumSet) { return ((EnumSet<E>)c).clone(); } else { if (c.isEmpty()) throw new IllegalArgumentException("Collection is empty"); Iterator<E> i = c.iterator(); E first = i.next(); EnumSet<E> result = EnumSet.of(first); while (i.hasNext()) result.add(i.next()); return result; } } /** * 创建一个枚举集合，其元素与 s 相同 * @param s the enum set from whose complement to initialize this enum set * @throws NullPointerException if <tt>s</tt> is null */ public static <E extends Enum<E>> EnumSet<E> complementOf(EnumSet<E> s) { EnumSet<E> result = copyOf(s); result.complement(); return result; } /** * 1 个元素枚举集合 * * @param e the element that this set is to contain initially * @throws NullPointerException if <tt>e</tt> is null * @return an enum set initially containing the specified element */ public static <E extends Enum<E>> EnumSet<E> of(E e) { EnumSet<E> result = noneOf(e.getDeclaringClass()); result.add(e); return result; } /** * 2 个元素枚举集合 * * @param e1 an element that this set is to contain initially * @param e2 another element that this set is to contain initially * @throws NullPointerException if any parameters are null * @return an enum set initially containing the specified elements */ public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2) { EnumSet<E> result = noneOf(e1.getDeclaringClass()); result.add(e1); result.add(e2); return result; } /** * 3 个元素枚举集合 * * @param e1 an element that this set is to contain initially * @param e2 another element that this set is to contain initially * @param e3 another element that this set is to contain initially * @throws NullPointerException if any parameters are null * @return an enum set initially containing the specified elements */ public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2, E e3) { EnumSet<E> result = noneOf(e1.getDeclaringClass()); result.add(e1); result.add(e2); result.add(e3); return result; } /** * 4 个元素枚举集合 * @param e1 an element that this set is to contain initially * @param e2 another element that this set is to contain initially * @param e3 another element that this set is to contain initially * @param e4 another element that this set is to contain initially * @throws NullPointerException if any parameters are null * @return an enum set initially containing the specified elements */ public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2, E e3, E e4) { EnumSet<E> result = noneOf(e1.getDeclaringClass()); result.add(e1); result.add(e2); result.add(e3); result.add(e4); return result; } /** * 5 个元素枚举集合 * * @param e1 an element that this set is to contain initially * @param e2 another element that this set is to contain initially * @param e3 another element that this set is to contain initially * @param e4 another element that this set is to contain initially * @param e5 another element that this set is to contain initially * @throws NullPointerException if any parameters are null * @return an enum set initially containing the specified elements */ public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2, E e3, E e4, E e5) { EnumSet<E> result = noneOf(e1.getDeclaringClass()); result.add(e1); result.add(e2); result.add(e3); result.add(e4); result.add(e5); return result; } /** * n 个元素枚举集合 * * @param first an element that the set is to contain initially * @param rest the remaining elements the set is to contain initially * @throws NullPointerException if any of the specified elements are null, * or if <tt>rest</tt> is null * @return an enum set initially containing the specified elements */ @SafeVarargs public static <E extends Enum<E>> EnumSet<E> of(E first, E... rest) { EnumSet<E> result = noneOf(first.getDeclaringClass()); result.add(first); for (E e : rest) result.add(e); return result; } /** * 区间内元素的 枚举集合 * * @param from the first element in the range * @param to the last element in the range * @throws NullPointerException if {@code from} or {@code to} are null * @throws IllegalArgumentException if {@code from.compareTo(to) > 0} * @return an enum set initially containing all of the elements in the * range defined by the two specified endpoints */ public static <E extends Enum<E>> EnumSet<E> range(E from, E to) { if (from.compareTo(to) > 0) throw new IllegalArgumentException(from + " > " + to); EnumSet<E> result = noneOf(from.getDeclaringClass()); result.addRange(from, to); return result; } /** * Adds the specified range to this enum set, which is empty prior * to the call. */ abstract void addRange(E from, E to); /** * Returns a copy of this set. * * @return a copy of this set */ public EnumSet<E> clone() { try { return (EnumSet<E>) super.clone(); } catch(CloneNotSupportedException e) { throw new AssertionError(e); } } /** * Complements the contents of this enum set. */ abstract void complement(); /** * Throws an exception if e is not of the correct type for this enum set. */ final void typeCheck(E e) { Class eClass = e.getClass(); if (eClass != elementType && eClass.getSuperclass() != elementType) throw new ClassCastException(eClass + " != " + elementType); } /** * Returns all of the values comprising E. * The result is uncloned, cached, and shared by all callers. */ private static <E extends Enum<E>> E[] getUniverse(Class<E> elementType) { return SharedSecrets.getJavaLangAccess() .getEnumConstantsShared(elementType); } /** * This class is used to serialize all EnumSet instances, regardless of * implementation type. It captures their "logical contents" and they * are reconstructed using public static factories. This is necessary * to ensure that the existence of a particular implementation type is * an implementation detail. * * @serial include */ private static class SerializationProxy <E extends Enum<E>> implements java.io.Serializable { /** * The element type of this enum set. * * @serial */ private final Class<E> elementType; /** * The elements contained in this enum set. * * @serial */ private final Enum[] elements; SerializationProxy(EnumSet<E> set) { elementType = set.elementType; elements = set.toArray(ZERO_LENGTH_ENUM_ARRAY); } private Object readResolve() { EnumSet<E> result = EnumSet.noneOf(elementType); for (Enum e : elements) result.add((E)e); return result; } private static final long serialVersionUID = 362491234563181265L; } Object writeReplace() { return new SerializationProxy<>(this); } // readObject method for the serialization proxy pattern // See Effective Java, Second Ed., Item 78. private void readObject(java.io.ObjectInputStream stream) throws java.io.InvalidObjectException { throw new java.io.InvalidObjectException("Proxy required"); }}总结
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