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.熟悉C, C++, C#, 或 Pascal人应该对列举有所了解,先看个例子:

    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,如 :

    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
    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:

    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.
    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:

    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.