java中EnumSet抽象类的示例分析

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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> extends AbstractSet  implements Cloneable, java.io.Serializable{  /**   * 元素类型   */  final Class elementType;  /**   * 通过数组存储元素    */  final Enum[] universe;  private static Enum[] ZERO_LENGTH_ENUM_ARRAY = new Enum[0];  EnumSet(ClasselementType, 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 elementType is null   */  public static > EnumSet noneOf(Class 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 elementType is null   */  public static > EnumSet allOf(Class elementType) {    EnumSet 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 s is null   */  public static > EnumSet copyOf(EnumSet 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 c is not an   *   EnumSet instance and contains no elements   * @throws NullPointerException if c is null   */  public static > EnumSet copyOf(Collection c) {    if (c instanceof EnumSet) {      return ((EnumSet)c).clone();    } else {      if (c.isEmpty())        throw new IllegalArgumentException("Collection is empty");      Iterator i = c.iterator();      E first = i.next();      EnumSet 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 s is null   */  public static > EnumSet complementOf(EnumSet s) {    EnumSet 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 e is null   * @return an enum set initially containing the specified element   */  public static > EnumSet of(E e) {    EnumSet 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 > EnumSet of(E e1, E e2) {    EnumSet 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 > EnumSet of(E e1, E e2, E e3) {    EnumSet 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 > EnumSet of(E e1, E e2, E e3, E e4) {    EnumSet 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 > EnumSet of(E e1, E e2, E e3, E e4,                          E e5)  {    EnumSet 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 rest is null   * @return an enum set initially containing the specified elements   */  @SafeVarargs  public static > EnumSet of(E first, E... rest) {    EnumSet 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 > EnumSet range(E from, E to) {    if (from.compareTo(to) > 0)      throw new IllegalArgumentException(from + " > " + to);    EnumSet 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 clone() {    try {      return (EnumSet) 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[] getUniverse(Class 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 >    implements java.io.Serializable  {    /**     * The element type of this enum set.     *     * @serial     */    private final Class elementType;    /**     * The elements contained in this enum set.     *     * @serial     */    private final Enum[] elements;    SerializationProxy(EnumSet set) {      elementType = set.elementType;      elements = set.toArray(ZERO_LENGTH_ENUM_ARRAY);    }    private Object readResolve() {      EnumSet 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");  }}

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