scala学习笔记（四）——隐式转换

隐式参数：
1：关键字 implicit
2：作用域：先去找全局的，再找局部的
3：要找唯一能匹配上的，如果有多个条件都满足，就报错。

4：implicit 都需要在object里面去使用

隐士转换的发生的时机：
1）当一个对象去调用某个方法，但是这个对象并不具备这个方法。

a: Int RichInt (源码)

b：File RichFile (《快学scala》)

package day4

class MyFile(var pp:String)

class MyRichFile(var p:String){
  def path: Unit ={
    println("ok:" + p)
  }
}

object implicit_2 {
  implicit def aa(a:MyFile)=new MyRichFile(a.pp)

  def main(args: Array[String]): Unit = {
    val file = new MyFile("yes")
    file.path
  }

}

c：超人变身

package day4

class SuperMan (var name:String,var age:Int){

}
class RichSuperMan(var name:String,var age:Int){

  def  fly: Unit ={
    println(s"name = $name and age = $age")
  }
}
object Test{
  implicit def rm(ss:SuperMan)=new RichSuperMan(ss.name,ss.age)
  def main(args: Array[String]): Unit = {

    val su = new SuperMan("zhangdan",55)
    su.fly


  }
}

2）调用某个方法的时候，这个方法确实也存在，存入的参数类型不匹配。

a：北京售票厅

package day4.implicit_test2

class Test {

}

class Person(var name:String)

class Student( name:String) extends Person(name:String)

class Older(name :String) extends Person(name :String)

object buyticket{
  def butt(p:Student): Unit ={
    println(p.name+"获得票了")
  }
  implicit  def aa(x:Person)=new Student(x.name)
  def main(args: Array[String]): Unit = {

    val person = new Person("zhangsan")
    val student = new Student("xiao ming")
    val older = new Older("lao wang")

//    butt(person)
    butt(older)

  }
}

3）视图边界
A <% B A必须是B的子类，如果不是，会触发隐士转换，转换成为B

package day4.implicit_test3

class Person(var name:String){
  def sayHello: Unit ={
    println(s"hello my name is $name")
  }
  def makeFriends(p:Person): Unit ={
    sayHello
    p.sayHello
  }
}
class Student (name:String) extends Person(name :String)

class Dog(var name:String)

class MakeFriends [T <% Person]{
  def paly(p1:Person,p2:Person): Unit ={
    p1.makeFriends(p2)
  }

}
object Testtt{
  implicit def dog2person(d:Dog):Person={
      new Person(d.name)
  }
  def main(args: Array[String]): Unit = {

    val dds = new Person("dds")
    val ss = new Student("ss")
    val dogDog = new Dog("dog")
    val mak = new MakeFriends[Person]
    mak.paly(dds,ss)
    mak.paly(dds,dogDog)

  }
}

上界：

package day4.implicit_test3

class Test1[T<:Comparable[T]] {
  def shuai(b1:T,b2:T): T ={
    if (b1.compareTo(b2) < 0)
      b1
    else
      b2
  }
}
object TTT{
  def main(args: Array[String]): Unit = {
    val zs = new Boy("zs",13)
    val ls = new Boy("ls",44)
    val p = new Test1[Boy]
    val boy = p.shuai(zs,ls)
    println(boy.name + "\t" + boy.value)
  }
}

下界：

package day4.implicit_test3

class A (var name:String)
class B (name:String) extends A( name:String)
class C (name:String) extends B( name:String)
class D (name:String)extends C( name:String)

class GetIdCard {
  def getCard[T>:C](a:T){
    println(" you get it")
  }

}
object ttt{
  def main(args: Array[String]): Unit = {
    val card = new GetIdCard
    card.getCard[C](new C("myself"))
  }
}

协变：
参加英雄联盟大赛父类 -》子类来了也可以
逆变：
上海大师赛（斯诺克的比赛）子类（业余） --》结果父类（丁俊晖）来了也可以。

package day4.implicit_test3

class A (var name:String)
class B (name:String) extends A( name:String)
class C (name:String) extends B( name:String)
class D (name:String)extends C( name:String)

class GetIdCard {
  def getCard[T>:C](a:T){
    println(" you get it")
  }

}
object ttt{
  def main(args: Array[String]): Unit = {
    val card = new GetIdCard
    card.getCard[C](new C("myself"))
  }
}

package day4.implicit_test3

class A (var name:String)
class B (name:String) extends A( name:String)
class C (name:String) extends B( name:String)
class D (name:String)extends C( name:String)

class GetIdCard {
  def getCard[T>:C](a:T){
    println(" you get it")
  }

}
object ttt{
  def main(args: Array[String]): Unit = {
    val card = new GetIdCard
    card.getCard[C](new C("myself"))
  }
}

package day4.implicit_test3

class A (var name:String)
class B (name:String) extends A( name:String)
class C (name:String) extends B( name:String)
class D (name:String)extends C( name:String)

class GetIdCard {
  def getCard[T>:C](a:T){
    println(" you get it")
  }

}
object ttt{
  def main(args: Array[String]): Unit = {
    val card = new GetIdCard
    card.getCard[C](new C("myself"))
  }
}

scala学习笔记（四）——隐式转换

猜你喜欢