Enumeration应该算是程序语言里面比较通用的一个类型，在scala中也存在这样的类型
Enumeration的定义
abstract class Enumeration (initial: Int) extends Serializable
Enumeration是一个抽象类，它定义四个value方法，来设置内部的值， 四个value方法如下定义：
/** Creates a fresh value, part of this enumeration. */ protected final def Value: Value = Value(nextId) /** Creates a fresh value, part of this enumeration, identified by the * integer `i`. * * @param i An integer that identifies this value at run-time. It must be * unique amongst all values of the enumeration. * @return Fresh value identified by `i`. */ protected final def Value(i: Int): Value = Value(i, nextNameOrNull) /** Creates a fresh value, part of this enumeration, called `name`. * * @param name A human-readable name for that value. * @return Fresh value called `name`. */ protected final def Value(name: String): Value = Value(nextId, name) /** Creates a fresh value, part of this enumeration, called `name` * and identified by the integer `i`. * * @param i An integer that identifies this value at run-time. It must be * unique amongst all values of the enumeration. * @param name A human-readable name for that value. * @return Fresh value with the provided identifier `i` and name `name`. */ protected final def Value(i: Int, name: String): Value = new Val(i, name)
知道如何设置Enum的值后，我们就可以尝试创建一个Enum了。
println("Step 1: How to create an enumeration") object Donut extends Enumeration { type Donut = Value val Glazed = Value("Glazed") val Strawberry = Value("Strawberry") val Plain = Value("Plain") val Vanilla = Value("Vanilla") }
上面的例子中，我们创建了一个Enum，并且设置了几个值。
下面我们看下怎么取到Enum的值：
println("\nStep 2: How to print the String value of the enumeration") println(s"Vanilla Donut string value = ${Donut.Vanilla}")
你可以看到如下的输出：
Step 2: How to print the String value of the enumeration Vanilla Donut string value = Vanilla
下面是怎么输出Enum的id：
println("\nStep 3: How to print the id of the enumeration") println(s"Vanilla Donut's id = ${Donut.Vanilla.id}")
结果如下：
Step 3: How to print the id of the enumeration Vanilla Donut's id = 3
怎么输出所有的Enum项呢？
println("\nStep 4: How to print all the values listed in Enumeration") println(s"Donut types = ${Donut.values}")
输出结果如下：
Step 4: How to print all the values listed in Enumeration Donut types = Donut.ValueSet(Glazed, Strawberry, Plain, Vanilla)
接下来，我们看下怎么打印出所有的Enum：
println("\nStep 5: How to pattern match on enumeration values") Donut.values.foreach { case d if (d == Donut.Strawberry || d == Donut.Glazed) => println(s"Found favourite donut = $d") case _ => None }
输出如下：
Step 5: How to pattern match on enumeration values Found favourite donut = Glazed Found favourite donut = Strawberry
最后，我们看下怎么改变Enum值的顺序：
println("\nStep 6: How to change the default ordering of enumeration values") object DonutTaste extends Enumeration{ type DonutTaste = Value val Tasty = Value(0, "Tasty") val VeryTasty = Value(1, "Very Tasty") val Ok = Value(-1, "Ok") } println(s"Donut taste values = ${DonutTaste.values}") println(s"Donut taste of OK id = ${DonutTaste.Ok.id}")
输出结果如下：
Step 6: How to change the default ordering of enumeration values Donut taste values = DonutTaste.ValueSet(Ok, Tasty, Very Tasty) Donut taste of OK id = -1
