Java 1.5新特性Enum的用法
Enum是enumeration(列举)的简写形式,包含在java.lang包中.public enum Season { winter, spring, summer, fall }
一个enum是定义一组值的对象,它可以包括零个或多个值成员.它是属于enum类型的,一个enum对象中不可有两个或多个相同的属性或值.在次之前的java程序员一般是 用接口的方法实现列举的,
public interface Season { static winter = 0; static spring = 1; //etc..}
引入了enum的java的列举的编写方便了许多,只须定义一个enum型的对象.enum对象的值都回自动获得一个数字值,从0开始,依次递增.看一个比较简单的enum实现的例子:
//EnumDemo.java/** * 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 title: */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 valuespublic static void main(String[] args) {for (Seasons s : Seasons.values()) {System.out.println(s);}}}
运行上述代码你回得到 以下结果:
winter
spring
summer
fall
Enum的属性调用:
下面的代码展示了调用enum对象的方法,这也是它通常的用法:
/** * 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 valuespublic static void main(String[] args) {// refer to the qualified valuedoIt(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添加属性和方法
enums也可以象一般的类一样添加方法和属性,你可以为它添加静态和非静态的属性或方法,这一切都象你在一般的类中做的那样.
/** * 在枚举类中加入方法 * File: EnumWithMethods.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;elsereturn summer;}}public static void main(String[] args) {System.out.println(Season.getBest());}}
就是这么的简单.但是有一点是需要注意的,那就是enums的值列表必须紧跟在enum声明,不然编译时将会出错.
Enums构造函数:
和类一样enums也可以有自己的构造函数,如下:
/** * 构造方式，创建枚举 title: **/public class EnumConstructor {public static void main(String[] a) {// call our enum using the values methodfor (Temp t : Temp.values())System.out.println(t + " is : " + t.getValue());}// make the enumpublic enum Temp {absoluteZero(-459), freezing(32), boiling(212), paperBurns(451);// constructor hereTemp(int value) {this.value = value;}// regular field?but make it final,// since that is the point, to make constantsprivate final int value;// regular get methodpublic int getValue() {return value;}}}
输出结果是:
absoluteZero is : -459
freezing is : 32
boiling is : 212
paperBurns is : 451
尽管enums有这么多的属性,但并不是用的越多越好,如果那样还不如直接用类来的直接.enums的优势在定义int最终变量仅当这些值有一定特殊含义时.但是如果你需要的是一个类,就定义一个类,而不是enum.
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