副标题#e#
Enum是enumeration(罗列)的简写形式,包括在java.lang包中.熟悉C,C++,C#,或Pascal人应该对罗列有所相识,先看个例子:
public enum Season { winter， spring， summer， fall }
一个enum是界说一组值的工具,它可以包罗零个或多个值成员.它是属于enum范例的,一个enum工具中不行有两个或多个沟通的属性或值.在次之前的java措施员一般是用接口的要领实现罗列的,如:
public interface Season {
static winter = 0；
static spring = 1； //etc……
}
引入了enum的java的罗列的编写利便了很多,只须界说一个enum型的工具.enum工具的值都回自动得到一个数字值,从0开始,依次递增.看一个较量简朴的enum实现的例子:
EnumDemo.java
package net.javagarage.enums；
/*
We can loop over the values we put into the enum
using the values（） method.
Note that the enum Seasons is compiled into a
separate unit， called EnumDemo$Seasons.class
*/
public class EnumDemo {
/*declare the enum and add values to it. note that， like in C#， we don't use a ； to
end this statement and we use commas to separate the values */
private enum Seasons { winter， spring，
summer， fall }
//list the values
public static void main（String[] args） {
for （Seasons s ： Seasons.values（））{
System.out.println（s）；
}
}
}
运行上述代码你回获得以下功效:
winter
spring
summer
fall
#p#副标题#e#
Enum的属性挪用:
下面的代码展示了挪用enum工具的要领,这也是它凡是的用法:
package net.javagarage.enums;
/*
File: EnumSwitch.java
Purpose: show how to switch against the values in an enum.
*/
public class EnumSwitch {
private enum Color { red, blue, green }
//list the values
public static void main(String[] args) {
//refer to the qualified value
doIt(Color.red);
}
/*note that you switch against the UNQUALIFIED name. that is, "case Color.red:" is a
compiler error */
private static void doIt(Color c){
switch (c) {
case red:
System.out.println("value is " + Color.red);
break;
case green:
System.out.println("value is " + Color.green);
break;
case blue:
System.out.println("value is : " + Color.blue);
break;
default :
System.out.println("default");
}
}
}
为enums添加属性和要领
enums也可以象一般的类一样添加要领和属性,你可觉得它添加静态和非静态的属性或要领,这一切都象你在一般的类中做的那样.
package net.javagarage.enums;
/*
File: EnumDemo.java
Purpose: show how to use an enum that also defines its own fields and methods
*/
public class EnumWithMethods {
//declare the enum and add values to it.
public enum Season {
winter, spring, summer, fall;
private final static String location = "Phoenix";
public static Season getBest(){
if (location.equals("Phoenix"))
return winter;
else
return summer;
}
public static void main(String[] args) {
System.out.println(Season.getBest());
}
}
就是这么的简朴.可是有一点是需要留意的,那就是enums的值列表必需紧跟在enum声明,否则编译时将会堕落.
Enums结构函数:
和类一样enums也可以有本身的结构函数,如下:
package net.javagarage.enums;
public class EnumConstructor {
public static void main(String[] a) {
//call our enum using the values method
for (Temp t : Temp.values())
System.out.println(t + " is : " + t.getValue());
}
//make the enum
public enum Temp {
absoluteZero(-459), freezing(32),
boiling(212), paperBurns(451);
//constructor here
Temp(int value) {
this.value = value;
}
//regular field?but make it final,
//since that is the point, to make constants
private final int value;
//regular get method
public int getValue() {
return value;
}
}
}
输出功效是:
absoluteZerois:-459
freezingis:32
boilingis:212
paperBurnsis:451
尽量enums有这么多的属性,但并不是用的越多越好,假如那样还不如直接用类来的直接.enums的优势在界说int最终变量仅当这些值有必然非凡寄义时.可是假如你需要的是一个类,就界说一个类,而不是enum.
