scala之类型参数

例子：
class Student[T,V](val localId: T,val localId2:V) {
def getSchoolId(hukouId: T,hukouId2:V) = "S-" + hukouId + "-" + hukouId2+"-"localId+"-"+localId2
}

val leo = new Student[Int,String](111,"222")
leo.getSchoolId(222,"222")

3.泛型函数

含义：泛型类一样，在scala中同属于一等公民
结构：
def getCard[T](v:T)={}

例子：
def getCard[T](content: T) = {
if(content.isInstanceOf[Int]) "card: 001, " + content
else if(content.isInstanceOf[String]) "card: this is your card, " + content
else "card: " + content
}

getCard[String]("hello world")

4.上边界Bounds，下边界Bounds

含义：
（1）边界：限定于有父子关系的两个类
（2）上，下：限定于该类型，或者该类型的子类，或者父类（包含关系）

适用范围：限定方法，限定类均可

例子：在派对上交朋友
class Person(val name: String) {
def sayHello = println("Hello, I'm " + name)
def makeFriends(p: Person) {
sayHello
p.sayHello
}
}
class Student(name: String) extends Person(name)
class Party[T <: Person](p1: T, p2: T) {
def play = p1.makeFriends(p2)
}

def getCard[T<:Person](content: T,content2:T) = {
println(content.makeFriends(content2))
}

例子：领身份证
class Father(val name: String)
class Child(name: String) extends Father(name)

def getIDCard[R >: Child](person: R) {
if (person.getClass == classOf[Child]) println("please tell us your parents' names.")
else if (person.getClass == classOf[Father]) println("sign your name for your child's id card.")
else println("sorry, you are not allowed to get id card.")
}

5.View Bounds 限定类

含义：相当于父子类的加强版
（1）支持有父子关系的多种类型
（2）支持“被隐式转换后”的类型判断

结构：
class Party[T <% Person](p1: T, p2: T)
比较：冒号“:” 替换为百分号 “%”

例子：跟小狗交朋友
class Person(val name: String) {
def sayHello = println("Hello, I'm " + name)
def makeFriends(p: Person) {
sayHello
p.sayHello
}
}
class Student(name: String) extends Person(name)
class Dog(val name: String) { def sayHello = println("Wang, Wang, I'm " + name) }

implicit def dog2person(dog: Object): Person = if(dog.isInstanceOf[Dog]) {val _dog = dog.asInstanceOf[Dog]; new Person(_dog.name) } else Nil

class Party[T <% Person](p1: T, p2: T) {
def play = p1.makeFriends(p2)
}

var leo = new Student("leo")
var dog = new Dog("wangcai")
var party = new Party(leo,dog)
party.play
执行结果比较慢

6.Context Bounds

含义： scala使用到上下文中的隐式值以及注入
特点：更加接洽与scala内置类的应用于比较

结构：
class Calculator[T: Ordering] (val number1: T, val number2: T) {
def max(implicit order: Ordering[T]) = 方法块儿（order.compare(number,number2)）
}

例子：
class Calculator[T: Ordering] (val number1: T, val number2: T) {
def max(implicit order: Ordering[T]) = if(order.compare(number1, number2) > 0) number1 else number2
}
var cal = new Calculator(1,24)
cal.max // 即可比较大小

7.Manifest Context Bounds

含义：实例化一个泛型数组，就必须使用Manifest Context Bounds
特点：针对于数组，集合而言（前面是针对单个对象）

例子：
class Meat(val name: String)
class Vegetable(val name: String)

def packageFood[T: Manifest] (food: T*) = {
val foodPackage = new Array[T](food.length)
for(i <- 0 until food.length) foodPackage(i) = food(i)
foodPackage
}

val v1 = new Vegetable("tudou")
val v2 = new Vegetable("doufu")

val packageFood = packageFood(v1,v2)

8.scala中的协变，逆变

含义：scala依据对象中传递的参数来协从的判断对象之间的从属关系
例子：Java中，如果有Professional是Master的子类，那么Card[Professionnal]是不是Card[Master]的子类
特点：更加灵活,直接用父子类，来对别的类的对象们进行了上下关系的区分

结构：
class Card[+T]()
class Card[-T]()
+ 表示T和T的子类
- 表示T和T的父类

例子：
class Master
class Professional extends Master

// 大师以及大师级别以下的名片都可以进入会场
class Card[+T] (val name: String)

def enterMeet(card: Card[Master]) {
println("welcome to have this meeting!")
}

val card1 = new Card[Master]("Tom")
val card2 = new Card[Professional]("Leo")
enterMeet(card1) OK
enterMeet(card2) OK

例子2：
class Master
class Professional extends Master

class Card[-T] (val name: String)
def enterMeet(card: Card[Master]) {
println("welcome to have this meeting!")
}

val card1 = new Card[Master]("Tom")
val card2 = new Card[Professional]("Leo")
enterMeet(card1) OK
enterMeet(card2) No

9.Existential Type

特点：特殊的类型占位符，表示在声明时，必须限定某一个类型

例子：
Array[_] = Array[T] forSome { type T }

1.何为泛型

2.泛型类