1. 关于Java Enum: 学过C/C++等语言的人,应该都对Enum类型略知一二。Enum一般用来表示一组相同类型的常量。如性别、日期、月份、颜色等。对这些属性用常量的好处是显而易见的,不仅可以保证单例,且比较时候可以用”==”来替换equals。是一种好的习惯。JDK1.5之前没有Enum这个类型,那时候一般用接口常量来替代。有了JavaEnum之后,可以更贴近的表示这种常量。
2. 如何使用Java Enum 简单的用法:JavaEnum简单的用法一般用于代表一组常用常量,可用来代表一类相同类型的常量值。如:
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性别: public
enum SexEnum {
male, female; } 颜色: public
enum Color {
RED, BLUE,GREEN,BLACK; } |
枚举对象里面的值都必须是唯一的。
可以通过Enum类型名直接引用该常量,如SexEnum.male,Color.RED.
复杂用法:Java为枚举类型提供了一些内置的方法,同事枚举常量还可以有自己的方法。可以很方便的遍历枚举对象,看个下面的例子:
1. 代码一 WeekDay.java:
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public enum WeekDay {
Mon( "Monday" ), Tue( "Tuesday" ), Wed( "Wednesday" ), Thu( "Thursday" ), Fri(
"Friday" ), Sat( "Saturday" ), Sun( "Sunday" );
private
final String day;
private
WeekDay(String day) {
this .day = day;
} public
static void printDay( int
i){
switch (i){
case 1 : System.out.println(WeekDay.Mon); break ;
case 2 : System.out.println(WeekDay.Tue); break ;
case 3 : System.out.println(WeekDay.Wed); break ;
case 4 : System.out.println(WeekDay.Thu); break ;
case 5 : System.out.println(WeekDay.Fri); break ;
case 6 : System.out.println(WeekDay.Sat); break ;
case 7 : System.out.println(WeekDay.Sun); break ;
default :System.out.println( "wrong number!" );
} } public
String getDay() {
return
day; } }
2 . 代码二 WeekDayTest.java:
public
class WeekDayTest {
public
static void main(String args[]) {
for (WeekDay day : WeekDay.values()) {
System.out.println(day + "====>"
+ day.getDay()); } WeekDay.printDay( 5 );
} } 输出结果为: Mon====>Monday Tue====>Tuesday Wed====>Wednesday Thu====>Thursday Fri====>Friday Sat====>Saturday Sun====>Sunday Fri |
3. Java Enum原理
Java Enum类型的语法结构尽管和java类的语法不一样,应该说差别比较大。但是经过编译器编译之后产生的是一个class文件。该class文件经过反编译可以看到实际上是生成了一个类,该类继承了java.lang.Enum<E>.
WeekDay经过反编译(javap WeekDay命令)之后得到的内容如下(去掉了汇编代码):
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public final class WeekDay extends
java.lang.Enum{
public static final WeekDay Mon;
public static final WeekDay Tue;
public static final WeekDay Wed;
public static final WeekDay Thu;
public
static final WeekDay Fri;
public
static final WeekDay Sat;
public
static final WeekDay Sun;
static
{};
public
static void printDay( int );
public
java.lang.String getDay();
public
static WeekDay[] values();
public
static WeekDay valueOf(java.lang.String);
} |
所以实际上Enum类型就是以Java类来实现的,没有什么新的特点,只不过java编译器帮我们做了语法的解析和编译。完全也可以自己实现。但是既然有这样方便一个东西,当然会去用了。
使用实例:
1》:以Class定义的
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public class PCUEnum { public
static void main(String[] args) {
System.out .println(PCUEnum.TaskStatus.get(PCUEnum.TaskStatus.DELETED)); }
public enum TaskStatus { /
/ 1 :等待执行 2 :正在执行 3 :执行完毕 4 :执行失败 5 :暂停 100 :已经删除 101 :已经送审 NOTINQUEUE,WAITING, EXECUTING, EXECUTED, FAILED, SUSPEND, DELETED,WAITING_AUDIT;
public
static int get(TaskStatus s) {
int result = 0 ; switch
(s) { case
NOTINQUEUE: result= 0 ; break ; case
WAITING: result = 1 ; break ; case
EXECUTING: result = 2 ; break ; case
EXECUTED: result = 3 ; break ; case
FAILED: result = 4 ; break ; case
SUSPEND: result = 5 ; break ; case
DELETED: result = 100 ; break ; case
WAITING_AUDIT: result = 101 ; break ; } return
result;
} }
}
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1.1》:以类为实例:
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public class EnumClass {
enum explore { HERE, THERE } enum
WeekDay { Mon( "Monday" ), Tue( "Tuesday" ), Wed( "Wednesday" ), Thu( "Thursday" ), Fri( "Friday" ), Sat( "Saturday" ), Sun( "Sunday" ), Wro( "Wrong day" );
private
String day;
WeekDay(String day){ this .day = day; }
public String getDay() { return
day; } } public
static void main(String[] args) { System.out.println(EnumClass.explore.HERE); System.out.println( "--------" ); for (EnumClass.WeekDay day : EnumClass.WeekDay.values()) { System.out.println(day.getDay());
}
}
}
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2》:以Enum定义的
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package
com.zhou.test;
public enum TaskEnumStatus {
NOTINQUEUE( 1 ),WAITING( 2 ), EXECUTING( 3 ), EXECUTED( 4 ), FAILED( 5 ), SUSPEND( 6 ), DELETED( 7 ),WAITING_AUDIT( 8 );
private
int
i;
private
TaskEnumStatus( int
i) {
this .i = i;
}
public
int getEnumStatus() {
return
i;
}
} public
static void main(String[] args) {
System.out.println(TaskEnumStatus.NOTINQUEUE + "="
+ TaskEnumStatus.NOTINQUEUE.getEnumStatus());
}
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2.1》:以Enum定义
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public enum UserStatusEnum {
DISABLE( "disable" ), ENABLE( "enable" ); private
String value;
UserStatusEnum(String value){ this .value = value;
}
public
String getValue() {
return
value;
} public
String toString() {
return
value;
} public
static void main(String[] args) {
System.out.println(UserStatusEnum.DISABLE); }
} |
2.2》:以Enum定义
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public enum NumberEnum {
CONST_FOUR( 4 ), CONST_ENIGHT( 8 ), CONST_NINE( 999999 ); private
final int value;
NumberEnum( int
value) {
this .value = value;
} public
int getValue() {
return
value;
} public
static void main(String[] args) {
System.out.println(NumberEnum.CONST_ENIGHT.getValue());
}
} |
原文地址:http://blog.sina.com.cn/s/blog_52fea7b60100phjl.html
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