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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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