使用implicitly demo

 

泛型:  Context Bounds

 

//  //定义一个隐式值, 这个值不能少, 要不找不到比较的对象
  implicit val personCompartor = new Ordering[Person] {
    override def compare(p1: Person, p2: Person): Int = {
      p1.age - p2.age
    }
  }

  def main(args: Array[String]): Unit = {

    val jack = new Person("jack", 20)
    val tom = new Person("tom", 30)

    val compareComm1 = new CompareComm(jack, tom)
    println(compareComm1.greater)
    println("---------------------")

    val compareComm2 = new CompareComm2(jack, tom)
    println(compareComm2.geatter)

    println("--------------------------")
    val compareComm3 = new CompareComm3(jack, tom)
    println(compareComm3.greatter)

  }

}


// 一个普通漫的personl类
class Person(val name: String, val age: Int) {
  override def toString: String = this.name + "\t" + this.age
}

/** 方式1
 * implicit comparetor: Ordering[T] 是一个隐式参数
 * 前面Ordered , Ordering
 * Ordered和Ordering的区别
 * Ordering继承了java中的Comparator接口，而Ordered继承了java的Comparable接口。
 * 在java中的Comparator是一个外部比较器（需要定义一个类来实现比较器），而Comparable则是一个内部比较器，在类内部重载compareTo函数。
 *
 */

class CompareComm[T: Ordering](obj1: T, obj2: T)(implicit comparetor: Ordering[T]) {

  def greater = if (comparetor.compare(obj1, obj2) > 0) obj1 else obj2
}


/**
 * 方式二
 * 隐式参数也可以直接写到方法中
 */

class CompareComm2[T: Ordering](obj1: T, obj2: T) {
  def geatter = {
    def f1(implicit comparetor: Ordering[T]) = comparetor.compare(obj1, obj2)

    if (f1 > 0) obj1 else obj2
  }
}

/**
 * 方式3,使用implicitly语法糖，最简单(推荐使用)
 */


class CompareComm3[T: Ordering](obj1: T, obj2: T) {
  def greatter = {
    //发生隐式转换，获取到隐式值 personComparetor
    val comparetor = implicitly[Ordering[T]]

    if (comparetor.compare(obj1, obj2) > 0) obj1 else obj2

  }
}

 

　　

模式匹配日志:

  //标准模式匹配, 可以在匹配中读取变量名称, 模式中也可是设置守卫, 可以变量赋值_newVa
  def judgeGrade(name: String, grade: String) {
    grade match {
      case "A" => println(name + ", you are excellent")
      case "B" => println(name + ", you are good")
      case "C" => println(name + ", you are just so so")
      case _newValu if name == "leo" => println(name + ", you are a good boy, come on ,_newValu: " + _newValu)
      case _ => println("you need to work harder")
    }
  }


  judgeGrade("leo", "D")


  //类型模式匹配
  def test(e: Exception): Unit = {
    e match {
      case e1: IllegalArgumentException => println("IllegualArgument")
      case e2: FileNotFoundException => println("FileNotFoundExceptino")
      case e3: NullPointerException => println("NullPointer")
      case _: Exception => println("common Exception")
    }

  }

  //对 Array 进行模式匹配
  def greeting(arr: Array[String]) {
    arr match {
      case Array("Leo") => println("Hi, Leo!")
      case Array(girl1, girl2, girl3) => println("Hi, girls, nice to meet you. " + girl1 + " and " + girl2 + " and " + girl3)
      case Array("Leo", _*) => println("Hi, Leo, please introduce your friends to me.")
      case _ => println("hey, who are you?")
    }
  }

  //对 List 进行模式匹配
  def greeting(list: List[String]) {
    list match {
      case "Leo" :: Nil => println("Hi, Leo!") //一个元素, 后面是 nil
      case girl1 :: girl2 :: girl3 :: Nil => println("Hi, girls, nice to meet you. " + girl1 + " and " + girl2 + " and " + girl3)
      case "Leo" :: tail => println("Hi, Leo, please introduce your friends to me.")
      case _ => println("hey, who are you?")
    }
  }

  //case Class 模式匹配
  class Person

  case class Teacher(name: String, subject: String) extends Person

  case class Student(name: String, classroom: String) extends Person

  def judgeIdentify(p: Person) {
    p match {
      case Teacher(name, subject) => println("Teacher, name is " + name + ", subject is " + subject)
      case Student(name, classroom) => println("Student, name is " + name + ", classroom is " + classroom)
      case _ => println("Illegal access, please go out of the school!")
    }
  }


  //Option 模式匹配
  val grades = Map("Leo" -> "A", "Jack" -> "B", "Jen" -> "C")

  def getGrade(name: String) {
    val grade = grades.get(name)
    grade match {
      case Some(grade) => println("your grade is " + grade)
      case None => println("Sorry, your grade information is not in the system")
    }
  }