scala判断语句

1.if 语句

object Test {
   def main(args: Array[String]) {
      var x = 10;

      if( x < 20 ){
         println("x < 20");
      }
   }
}

结果
x < 20

2.if...else 语句

object Test {
   def main(args: Array[String]) {
      var x = 30;

      if( x < 20 ){
         println("x 小于 20");
      }else{
         println("x 大于 20");
      }
   }
}

结果
x 大于 20

3.if...else if...else 语句

object Test {
   def main(args: Array[String]) {
      var x = 30;

      if( x == 10 ){
         println("X 的值为 10");
      }else if( x == 20 ){
         println("X 的值为 20");
      }else if( x == 30 ){
         println("X 的值为 30");
      }else{
         println("无法判断 X 的值");
      }
   }
}

结果
X 的值为 30

4.while 循环

object Test {
   def main(args: Array[String]) {
      // 局部变量
      var a = 10;

      // while 循环执行
      while( a < 20 ){
         println( "Value of a: " + a );
         a = a + 1;
      }
   }
}

结果
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

5.do...while 循环

object Test {
   def main(args: Array[String]) {
      // 局部变量
      var a = 10;

      // do 循环
      do{
         println( "Value of a: " + a );
         a = a + 1;
      }while( a < 20 )
   }
}

结果
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

6.for循环

import scala.util.control.Breaks.{break, breakable}


object HelloWord {
  def main(args: Array[String]) {
    // for 循环
    breakable {
      for (a <- 1 to 10) { // 1 to 10 1到10列表  包含10    1 until 10 不包含10
        if (a == 9) {
          break   // 结束循环
        }
        println("Value of a: " + a);
      }
    }
  }
}

结果
Value of a: 1
Value of a: 2
Value of a: 3
Value of a: 4
Value of a: 5
Value of a: 6
Value of a: 7
Value of a: 8

7.for 使用 yield

object Test {
   def main(args: Array[String]) {
      var a = 0;
      val numList = List(1,2,3,4,5,6,7,8,9,10);

      // for 循环
      var retVal = for{ a <- numList 
                        if a != 3; if a < 8
                      }yield a

      // 输出返回值
      for( a <- retVal){
         println( "Value of a: " + a );
      }
   }
}

结果
value of a: 1
value of a: 2
value of a: 4
value of a: 5
value of a: 6
value of a: 7

8.case的用法

object HelloWord {
  def main(args: Array[String]) {
    // 1.简单匹配，值匹配
    val bools = List(true, false, "方法")
    for (bool <- bools) {
      bool match {
        case true => println("heads")
        case false => println("tails")
        case _ => println("something other than heads or tails (yikes!)") // 没匹配到
      }
    }
    // 2.类型匹配
    val sundries = List(23, "Hello", 8.5, 'q')
    for (sundry <- sundries) {
      sundry match {
        case i: Int => println("got an Integer: " + i)
        case s: String => println("got a String: " + s)
        case f: Double => println("got a Double: " + f)
        case other => println("got something else: " + other)
      }
    }
    // 3.根据顺序匹配
    val willWork = List(1, 3, 23, 90)
    val willNotWork = List(4, 18, 52)
    val empty = List()
    for (l <- List(willWork, willNotWork, empty)) {
      l match {
        case List(_, 3, _, _) => println("Four elements, with the 2nd being '3'.")
        case List(_*) => println("Any other list with 0 or more elements.")
      }
    }
    // 4.case里面用 guard 的数组匹配
    val tupA = ("Good", "Morning!")
    val tupB = ("Guten", "Tag!")
    for (tup <- List(tupA, tupB)) {
      tup match {
        case (thingOne, thingTwo) if thingOne == "Good" =>
          println("A two-tuple starting with 'Good'.")
        case (thingOne, thingTwo) => println("This has two things: " + thingOne + " and " + thingTwo)
      }
    }
    // 5.对象深度匹配
    case class Person(name: String, age: Int)
    val alice = new Person("Alice", 25)
    val bob = new Person("Bob", 32)
    val charlie = new Person("Charlie", 32)
    for (person <- List(alice, bob, charlie)) {
      person match {
        case Person("Alice", 25) => println("Hi Alice!")
        case Person("Bob", 32) => println("Hi Bob!")
        case Person(name, age) =>
          println("Who are you, " + age + " year-old person named " + name + "?")
      }
    }
    // 6.正则表达式匹配
    val BookExtractorRE =
      """Book: title=([^,]+),s+authors=(.+)""".r
    val MagazineExtractorRE = """Magazine: title=([^,]+),s+issue=(.+)""".r

    val catalog = List(
      "Book: title=Programming Scala, authors=Dean Wampler, Alex Payne",
      "Magazine: title=The New Yorker, issue=January 2009",
      "Book: title=War and Peace, authors=Leo Tolstoy",
      "Magazine: title=The Atlantic, issue=February 2009",
      "BadData: text=Who put this here??"
    )

    for (item <- catalog) {
      item match {
        case BookExtractorRE(title, authors) =>
          println("Book "" + title + "", written by " + authors)
        case MagazineExtractorRE(title, issue) =>
          println("Magazine "" + title + "", issue " + issue)
        case entry => println("Unrecognized entry: " + entry)
      }
    }
  }
}