(轉(zhuǎn)自
http://www.aygfsteel.com/dazuiba/archive/2006/08/04/j2se_enum.html)
1 定義在常量類中
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??? 經(jīng)常碰到要將枚舉類當(dāng)成常量使用的情況，這不僅可以將相關(guān)的常量定義到一個(gè)枚舉類中，而且還可以利用枚舉類強(qiáng)大而又靈活的功能，在加上編譯器內(nèi)置的支持，使得在eclipse下的編程更方便，引入的bug更少。
??? 一般規(guī)模的項(xiàng)目中都會(huì)用一個(gè)單獨(dú)的類來(lái)定義系統(tǒng)中用到的常量，起碼筆者經(jīng)歷的幾個(gè)項(xiàng)目都是有此種做法，該做法的好處就是便于集中管理，雖然這違背類封裝的原則，但鑒于其易用性，我們還是會(huì)常常這么做。
??? 例子：
public?class?SystemConstant?
{
????/**?*//**
?????*?金庫(kù) sourceortarget?系統(tǒng)相關(guān)
?????*/
????public?static?final?String?CASHWASTEBOOK_SOURCEORTARGET_SYS?=?"系統(tǒng)";
????/**?*//**
?????*?附件上傳路徑
?????*/?
????public?static?String?UPLOAD_ATTACHMENT_DIR="upload\\";
????public?static?String?CONFIG_DIR="config\\";
????/**?*//**
?????*?臨時(shí)文件路徑
?????*/
????public?static?String?TEMP_DIR="temp\\";
????/**?*//**
?????*?會(huì)員關(guān)系
?????*/
????public?static?enum?Relationship?{
????????GoodFriend("親密好友"),
????????CommonFriend("普通朋友"),
????????BLACK("不受歡迎");
????????private???String?v;
????????
????????Relationship(String?value)?{
??????????v?=?value;
????????}
????????@Override
????????public?String?toString()?{????????
????????????return?v;
????????}?
??????}??
????public?static?final?String?SUCCESS?=?"OK";
????/**?*//**用戶選擇管理員登錄*/
????public?static?final?String?MESSAGE_LOGIN_TYPEERROR1?=?"您不能選擇管理員登錄";
????/**?*//**管理員選擇會(huì)員或家長(zhǎng)登錄*/
????public?static?final?String?MESSAGE_LOGIN_TYPEERROR2?=?"您應(yīng)該選擇管理員登錄";
????/**?*//**會(huì)員或家長(zhǎng)重復(fù)登陸*/
????public?static?final?String?MESSAGE_LOGIN_REPEAT?=?"可能因?yàn)橐韵略颍鸁o(wú)法登陸系統(tǒng)\n\t１ 有人盜用您的帳號(hào)\n２?您的{0}正在使用本帳號(hào)";
????public?static?final?String?MESSAGE_LONGIN_PASSWORDERROR?=?"用戶名或密碼無(wú)效";
????public?static?final?String?MESSAGE_INSUFFICIENT_FUNDS?=?"您的帳戶余額不足";
????public?static?final?String?MESSAGE_MEMBER_ONLINETIME_FULL?=?"您今日的累計(jì)上線時(shí)間已超過(guò)１.５小時(shí)";
????/**?*//**會(huì)員每天最大登錄時(shí)限?單位分鐘?默認(rèn)90**/
????public?static?final?int?MEMBER_MAX_DAY_ONLINE_MINUTES?=?90;
????
}
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??? 可以看到，枚舉類型Relationship是定義一些會(huì)員關(guān)系之間的東東，其實(shí)我可以把它單獨(dú)定義一個(gè)類，或者放到Member(會(huì)員)這個(gè)類中，但綜合考慮，我還是覺(jué)得放到SystemConstant比較好，并且今后重構(gòu)SystemConstant，會(huì)添加從xml文件讀取屬性的功能。
?? ? 雖然Relationship是一個(gè)內(nèi)部類，但由于是靜態(tài)的，所以可以直接import,而無(wú)須每次都用SystemConstant.Relationship;
?例如：
?? ?public Relationship getRelationship() {
????????? ?return Relationship.valueOf(relationship);
?????? ?}
? 2 說(shuō)到從xml文件讀取屬性來(lái)動(dòng)態(tài)配置枚舉類，我下面就舉個(gè)例子，演示演示
???? 一些web系統(tǒng)中涉及到文件上傳，根據(jù)文件類型顯示相應(yīng)圖標(biāo)，并且有些jsp,asp等等的文件不允許上傳，下面就是一個(gè)滿足這種需求的枚舉類，它最大的特點(diǎn)就是可以從xml中讀取配置信息
/**?*//**
?*?系統(tǒng)中用到的文件擴(kuò)展名?枚舉類
?*?@author?zgy
?*
?*/
public?enum?FileExtension?{
????doc,?jsp,?jpeg,?jpg,?rar,?zip,?txt,unknown;
????private?boolean?allow;
?
????private?String?comment;
????private?String?iconPath;
????static?{
????????loadFromXml();?
????}?
????FileExtension()?{
????????this.iconPath?=?"\\"?+?name();
????????this.allow?=?true;
????????this.comment?=?"comment?for"?+?name();
????}????
????/**?*//**
?????*?從config目錄中l(wèi)oad
?????*?
?????*/
????private?static?void?loadFromXml()?{
????????try?{
????????????Document?doc?=?XmlUtil.parseXmlFile(SystemConstant.CONFIG_DIR
????????????????????+?"fileExtension.xml");
????????????NodeList?extensionList?=?doc.getElementsByTagName("FileExtension");
????????????for?(int?i?=?0;?i?<?extensionList.getLength();?i++)?{
????????????????Element?item?=?(Element)?extensionList.item(i);
????????????????String?name?=?item.getAttribute("name");
????????????????FileExtension?em?=?FileExtension.valueOf(name);
????????????????em.allow?=?Boolean.parseBoolean(item.getAttribute("allow"));
????????????????em.iconPath?=?item.getAttribute("iconPath");
????????????????em.comment?=?item.getAttribute("comment");?
????????????}
????????}?catch?(Exception?e)?{?
????????????throw?new?RuntimeException(e);
????????}
????}
????public?boolean?isAllow()?{
????????return?allow;
????}
????public?String?getComment()?{
????????return?comment;
????}?
????public?String?getUploadIcon()?{
????????return?iconPath;
????}
????public?static?void?main(String[]?args)?{
????????System.out.println(FileExtension.doc.comment);
????}
}
配置文件如下：config/fileExtension.xml
<?xml version="1.0" encoding="UTF-8"?>
<FileExtensions>
?<FileExtension name="doc" iconPath="doc.jpg" allow="true"?? comment="文本"/>
?<FileExtension name="jpg" iconPath="jpg.jpg" allow="true"?? comment=""/>
?<FileExtension name="jpeg" iconPath="jpeg.jpg" allow="true" comment=""/>
?<FileExtension name="rar" iconPath="rar.jpg" allow="true"?? comment=""/>
?<FileExtension name="zip" iconPath="zip.jpg" allow="true"?? comment=""/>
?<FileExtension name="txt" iconPath="txt.jpg" allow="true"?? comment=""/>
??? <FileExtension name="jsp" iconPath="jsp.jpg" allow="false"? comment=""/>
</FileExtensions>
可能系統(tǒng)中其他的一些枚舉類（比如1 中提到的RelationShip）也會(huì)用到非常類似的做法，這時(shí)候我們就可以重構(gòu)了，將一些共同的特點(diǎn)抽取到一個(gè)抽象類中。這將會(huì)在以后的文章中提到。
有不同的觀點(diǎn)，請(qǐng)聯(lián)系
come2u at gmail.com? ,歡迎交流。