Basic application of scala for

scala-for Application ：

Go straight to the code .

  def testfor01: Unit ={

    val nieces = List("emily", "hananh", "mercedes", "porsche")
    /*
     keyword yield：for In the loop yield The current element will be recorded ,
                  Save to collection , After the loop ends, the set is returned .
                 scala in for A loop has a return value , If what is being cycled is Map, Then it returns Map,
                  If what is being cycled is List, Is returned List, And so on 

    scala There are many ways to traverse a collection ：for loop 、foreach loop 、while loop 、map mapping 、flatmap etc. 

     Use to or until Conduct for loop ,to And until difference ：
        to: Including upper and lower limits , It's a closed interval 
        until： Excluding upper and lower limits , It's open range 
     */
    for (n <- nieces) yield println(n.capitalize)
    /*
        for (n <- nieces) such for In the derivation , Failed matches are quietly ignored 
     */
    nieces.foreach(nie => println(nieces.mkString))


    //2、for A loop can be used as a timer 
    println("------for as a timer------")
    val a = Array("apple", "banana", "orange")
    a.foreach(println)
    for (i <- 0 until a.length if i != 1) println(s"$i is ${a(i)}")


    //3、 Defensive sentences （for In circulation if Judge ）, here to  And until Same function 
    // Guard statements are usually used as filter sets , According to the specific requirements , You can use... In the set filter、take、drop And so on for loop 
    println("------  stay for There are in the loop if Statement nesting  ------")
    for (x <- 0 to 5 if x != 3) println(x)
    // stay for Nested in a loop if sentence , Multiple can be nested at the same time if sentence 
    for (wei_x <- 0 to 5 if wei_x % 2 == 0 if wei_x == 2) println(wei_x)


    System.out.println("------  Traverse Map aggregate  ------")
    // Traverse Map aggregate 
    val names = Map("fname" -> "Robert", "lname" -> "Goren")
    for ((k, v) <- names) println(s"key: $k, value: $v")
  }

     

  def testfor02: Unit ={

    val nieces = List("emily", "hananh", "mercedes", "porsche")

    //for deduction ： adopt for-yield Application for A loop has a return value .
    val str01: List[String] = for (n <- nieces if !n.contains("emily")) yield  n+" ... dd"
    str01.foreach(println)

    //for deduction ： stay yield When there are multiple lines of code in , Use in yield Using code blocks 
    val str02 = for (n <- nieces if ! n.contains("emily")) yield {
      val str = n+" ... dd"
      str
    }

    str02.foreach(println)

  }

  scala-for Attention during application for Is the inner loop an open interval or a closed interval , If you use for-yield The guards , it is to be noted that yield The return object of .