EnumSet抽象类源码解析

EnumSet

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");
    }
}