阅读EnumSet抽象类源码

2023-09-20 04:00:05 266

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

packagejava.util;

importsun.misc.SharedSecrets;


publicabstractclassEnumSet>extendsAbstractSet
implementsCloneable,java.io.Serializable
{
/**
*元素类型
*/
finalClasselementType;

/**
*通过数组存储元素
*/
finalEnum[]universe;

privatestaticEnum[]ZERO_LENGTH_ENUM_ARRAY=newEnum[0];

EnumSet(ClasselementType,Enum[]universe){
this.elementType=elementType;
this.universe=universe;
}

/**
*创造一个空的enumset并制定其元素类型
*@paramelementTypetheclassobjectoftheelementtypeforthisenum
*set
*@throwsNullPointerExceptionifelementTypeisnull
*/
publicstatic>EnumSetnoneOf(ClasselementType){
Enum[]universe=getUniverse(elementType);
if(universe==null)
thrownewClassCastException(elementType+"notanenum");

if(universe.length<=64)
returnnewRegularEnumSet<>(elementType,universe);
else
returnnewJumboEnumSet<>(elementType,universe);
}

/**
*创建一个包含所有在指定元素类型的元素的枚举set
*
*@paramelementTypetheclassobjectoftheelementtypeforthisenum
*set
*@throwsNullPointerExceptionifelementTypeisnull
*/
publicstatic>EnumSetallOf(ClasselementType){
EnumSetresult=noneOf(elementType);
result.addAll();
returnresult;
}

/**
*Addsalloftheelementsfromtheappropriateenumtypetothisenum
*set,whichisemptypriortothecall.
*/
abstractvoidaddAll();

/**
*创建一个枚举设置相同的元素类型与指定枚举set
*
*@paramstheenumsetfromwhichtoinitializethisenumset
*@throwsNullPointerExceptionifsisnull
*/
publicstatic>EnumSetcopyOf(EnumSets){
returns.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
*@paramcthecollectionfromwhichtoinitializethisenumset
*@throwsIllegalArgumentExceptionifcisnotan
*EnumSetinstanceandcontainsnoelements
*@throwsNullPointerExceptionifcisnull
*/
publicstatic>EnumSetcopyOf(Collectionc){
if(cinstanceofEnumSet){
return((EnumSet)c).clone();
}else{
if(c.isEmpty())
thrownewIllegalArgumentException("Collectionisempty");
Iteratori=c.iterator();
Efirst=i.next();
EnumSetresult=EnumSet.of(first);
while(i.hasNext())
result.add(i.next());
returnresult;
}
}

/**
*创建一个枚举集合，其元素与s相同
*@paramstheenumsetfromwhosecomplementtoinitializethisenumset
*@throwsNullPointerExceptionifsisnull
*/
publicstatic>EnumSetcomplementOf(EnumSets){
EnumSetresult=copyOf(s);
result.complement();
returnresult;
}

/**
*1个元素枚举集合
*
*@parametheelementthatthissetistocontaininitially
*@throwsNullPointerExceptionifeisnull
*@returnanenumsetinitiallycontainingthespecifiedelement
*/
publicstatic>EnumSetof(Ee){
EnumSetresult=noneOf(e.getDeclaringClass());
result.add(e);
returnresult;
}

/**
*2个元素枚举集合
*
*@parame1anelementthatthissetistocontaininitially
*@parame2anotherelementthatthissetistocontaininitially
*@throwsNullPointerExceptionifanyparametersarenull
*@returnanenumsetinitiallycontainingthespecifiedelements
*/
publicstatic>EnumSetof(Ee1,Ee2){
EnumSetresult=noneOf(e1.getDeclaringClass());
result.add(e1);
result.add(e2);
returnresult;
}

/**
*3个元素枚举集合
*
*@parame1anelementthatthissetistocontaininitially
*@parame2anotherelementthatthissetistocontaininitially
*@parame3anotherelementthatthissetistocontaininitially
*@throwsNullPointerExceptionifanyparametersarenull
*@returnanenumsetinitiallycontainingthespecifiedelements
*/
publicstatic>EnumSetof(Ee1,Ee2,Ee3){
EnumSetresult=noneOf(e1.getDeclaringClass());
result.add(e1);
result.add(e2);
result.add(e3);
returnresult;
}

/**
*4个元素枚举集合
*@parame1anelementthatthissetistocontaininitially
*@parame2anotherelementthatthissetistocontaininitially
*@parame3anotherelementthatthissetistocontaininitially
*@parame4anotherelementthatthissetistocontaininitially
*@throwsNullPointerExceptionifanyparametersarenull
*@returnanenumsetinitiallycontainingthespecifiedelements
*/
publicstatic>EnumSetof(Ee1,Ee2,Ee3,Ee4){
EnumSetresult=noneOf(e1.getDeclaringClass());
result.add(e1);
result.add(e2);
result.add(e3);
result.add(e4);
returnresult;
}

/**
*5个元素枚举集合
*
*@parame1anelementthatthissetistocontaininitially
*@parame2anotherelementthatthissetistocontaininitially
*@parame3anotherelementthatthissetistocontaininitially
*@parame4anotherelementthatthissetistocontaininitially
*@parame5anotherelementthatthissetistocontaininitially
*@throwsNullPointerExceptionifanyparametersarenull
*@returnanenumsetinitiallycontainingthespecifiedelements
*/
publicstatic>EnumSetof(Ee1,Ee2,Ee3,Ee4,
Ee5)
{
EnumSetresult=noneOf(e1.getDeclaringClass());
result.add(e1);
result.add(e2);
result.add(e3);
result.add(e4);
result.add(e5);
returnresult;
}

/**
*n个元素枚举集合
*
*@paramfirstanelementthatthesetistocontaininitially
*@paramresttheremainingelementsthesetistocontaininitially
*@throwsNullPointerExceptionifanyofthespecifiedelementsarenull,
*orifrestisnull
*@returnanenumsetinitiallycontainingthespecifiedelements
*/
@SafeVarargs
publicstatic>EnumSetof(Efirst,E...rest){
EnumSetresult=noneOf(first.getDeclaringClass());
result.add(first);
for(Ee:rest)
result.add(e);
returnresult;
}

/**
*区间内元素的枚举集合
*
*@paramfromthefirstelementintherange
*@paramtothelastelementintherange
*@throwsNullPointerExceptionif{@codefrom}or{@codeto}arenull
*@throwsIllegalArgumentExceptionif{@codefrom.compareTo(to)>0}
*@returnanenumsetinitiallycontainingalloftheelementsinthe
*rangedefinedbythetwospecifiedendpoints
*/
publicstatic>EnumSetrange(Efrom,Eto){
if(from.compareTo(to)>0)
thrownewIllegalArgumentException(from+">"+to);
EnumSetresult=noneOf(from.getDeclaringClass());
result.addRange(from,to);
returnresult;
}

/**
*Addsthespecifiedrangetothisenumset,whichisemptyprior
*tothecall.
*/
abstractvoidaddRange(Efrom,Eto);

/**
*Returnsacopyofthisset.
*
*@returnacopyofthisset
*/
publicEnumSetclone(){
try{
return(EnumSet)super.clone();
}catch(CloneNotSupportedExceptione){
thrownewAssertionError(e);
}
}

/**
*Complementsthecontentsofthisenumset.
*/
abstractvoidcomplement();

/**
*Throwsanexceptionifeisnotofthecorrecttypeforthisenumset.
*/
finalvoidtypeCheck(Ee){
ClasseClass=e.getClass();
if(eClass!=elementType&&eClass.getSuperclass()!=elementType)
thrownewClassCastException(eClass+"!="+elementType);
}

/**
*ReturnsallofthevaluescomprisingE.
*Theresultisuncloned,cached,andsharedbyallcallers.
*/
privatestatic>E[]getUniverse(ClasselementType){
returnSharedSecrets.getJavaLangAccess()
.getEnumConstantsShared(elementType);
}

/**
*ThisclassisusedtoserializeallEnumSetinstances,regardlessof
*implementationtype.Itcapturestheir"logicalcontents"andthey
*arereconstructedusingpublicstaticfactories.Thisisnecessary
*toensurethattheexistenceofaparticularimplementationtypeis
*animplementationdetail.
*
*@serialinclude
*/
privatestaticclassSerializationProxy>
implementsjava.io.Serializable
{
/**
*Theelementtypeofthisenumset.
*
*@serial
*/
privatefinalClasselementType;

/**
*Theelementscontainedinthisenumset.
*
*@serial
*/
privatefinalEnum[]elements;

SerializationProxy(EnumSetset){
elementType=set.elementType;
elements=set.toArray(ZERO_LENGTH_ENUM_ARRAY);
}

privateObjectreadResolve(){
EnumSetresult=EnumSet.noneOf(elementType);
for(Enume:elements)
result.add((E)e);
returnresult;
}

privatestaticfinallongserialVersionUID=362491234563181265L;
}

ObjectwriteReplace(){
returnnewSerializationProxy<>(this);
}

//readObjectmethodfortheserializationproxypattern
//SeeEffectiveJava,SecondEd.,Item78.
privatevoidreadObject(java.io.ObjectInputStreamstream)
throwsjava.io.InvalidObjectException{
thrownewjava.io.InvalidObjectException("Proxyrequired");
}
}

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阅读EnumSet抽象类源码

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