scala basic

第一个程序

//object是共生对象，相当于java的静态类
object HelloScala {

  def main(args: Array[String]){
    println("Hello Scala!!!A new World!!!")
    for(arg <- args) println(arg)  //循环打印参数
  }

}

 

流程控制

/**
      * scala中的if表达式是有值的！！ 这个Java是不一样的
      * 如果if后面没有else部分，默认的实现if else
      * {}中有多条语句，最后一条语句是计算结果
      * ｛｝代表一个语句块，语句快是有值的，值就是最后一条语句，返回类型应该设定成最后一句的类型
      */
     var age = 10
     val result = if (age >25) "worker" else "student"
     println(result)
     
     //else前后的内容一个是字符串，一个是数字，所以result2
     val result2 = if (age > 18) "Adult" else 1 
     
     //result3 类型是
     val result3 = if (age > 18) "Adult"
     println(result3)
     
     var x,y = 0
     var result4 = if(age < 18){
       x = x + 1
       y = y + 1
       x + y
     }else 0
     println(result4)
     
     //def to(end: Int): Range.Inclusive
     // 0.to(5) 也可以
     for(i <- 0 to 5  if i % 2 == 0){
        println(i) 
     }
    /*
     * 想跳出for的话，除了加入if守卫以外，还可以是用return关键字
     */
     var flag = true
     var sum = 0
     for (i <- 0 to 6 if flag){
       sum = sum + i
       if(5 == i) flag = false
     }
     println("sum = " + sum)

 

数组

import scala.collection.mutable.ArrayBuffer
//强大的scala的worksheet,即时显示执行结果（右边为自动显示结果）

object ScalaInAction {
  println("Welcome to the Scala worksheet")       //> Welcome to the Scala worksheet
   val b = ArrayBuffer[Int]()                     //> b  : scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
    b+=1                                          //> res0: learning.basics.ScalaInAction.b.type = ArrayBuffer(1)
    b+=(1,2,3)                                    //> res1: learning.basics.ScalaInAction.b.type = ArrayBuffer(1, 1, 2, 3)
    b++=Array(4,5)                                //> res2: learning.basics.ScalaInAction.b.type = ArrayBuffer(1, 1, 2, 3, 4, 5)
    b.insert(2, 6)
    b                                             //> res3: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 6, 2, 3,
    //去掉最后3位                                              //|  4, 5)
    b.trimEnd(3)
    b                                             //> res4: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 6, 2)
    b.insert(2,7,8,9)
    b                                             //> res5: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 7, 8, 9,
                                                  //|  6, 2)
    b.remove(2)                                   //> res6: Int = 7
    b                                             //> res7: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 8, 9, 6,
                                                  //|  2)
    b.remove(2,3)
    b                                             //> res8: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 2)
    b.toArray                                     //> res9: Array[Int] = Array(1, 1, 2)
    b                                             //> res10: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 2)
    for(i <- 0 until b.length) println(b(i))      //> 1
                                                  //| 1
                                                  //| 2
    val c = Array(2,3,4,7,9)                      //> c  : Array[Int] = Array(2, 3, 4, 7, 9)
    val result = for(item <-c) yield item + 1     //> result  : Array[Int] = Array(3, 4, 5, 8, 10)
    
//符合条件的乘以2 _ 代替符号 是很经典的用法
    val result1 =c.filter(_ % 2 == 0).map(2 * _)  //> result1  : Array[Int] = Array(4, 8)
    Array(2,4,6,8).sum                            //> res11: Int = 20
    
    val d = ArrayBuffer(1, 7, 2, 9)               //> d  : scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 7, 2, 9)
    val bSorted = d.sorted                        //> bSorted  : scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 7, 
                                                  //| 9)
    val e = Array(1, 7, 2, 9)                     //> e  : Array[Int] = Array(1, 7, 2, 9)
    scala.util.Sorting.quickSort(e)
    
    //参数为分隔符
    e.mkString(" and ")                           //> res12: String = 1 and 2 and 7 and 9
    e.mkString("<",",",">")                       //> res13: String = <1,2,7,9>
    
    val matrix = Array.ofDim[Double](3,4)         //> matrix  : Array[Array[Double]] = Array(Array(0.0, 0.0, 0.0, 0.0), Array(0.0,
                                                  //|  0.0, 0.0, 0.0), Array(0.0, 0.0, 0.0, 0.0))
    matrix(2)(1) = 42
    matrix                                        //> res14: Array[Array[Double]] = Array(Array(0.0, 0.0, 0.0, 0.0), Array(0.0, 0.
                                                  //| 0, 0.0, 0.0), Array(0.0, 42.0, 0.0, 0.0))
}

 

Map和Tuple

 val map = Map("book"->10,"gun"->18,"ipad"->1000)  
 // yield 给map每个元素赋值
 for((k,v) <- map) yield (k,v * 0.9)
  
  val scores = scala.collection.mutable.Map("Scala" -> 7, "Hadoop" -> 8, "Spark" -> 10 )
  
//getOrElse使用很普遍，当Hadoop为空的时候，返回0
  val hadoopScore = scores.getOrElse("Hadoop", 0)
  //追加元素
  scores += ("R" -> 9)
  //删除元素
  scores -= "Hadoop"
  
  val sortedScore = scala.collection.immutable.SortedMap("Scala" -> 7, "Hadoop" -> 8, "Spark" -> 10 )
  
  val tuple =(1,2,3.14,"Rocky","Spark","Flink")
  val third = tuple._3
  val (first,second,thirda,fourth,fifth,sixth) = tuple
  val (f, s, _, _, _,_) = tuple
  
  //通过大小写原则分类
  "Rocky Spark".partition(_.isUpper)
  
  val symbols = Array("[", "-", "]")
  val counts = Array(2,5,2)
  val pairs = symbols.zip(counts)
  for ((x,y) <- pairs) print(x*y)

 

 函数

object For_Function_Advanced {

  def main(args: Array[String]): Unit = {
    
//    for(i <- 1 to 2; j <- 1 to 2) print((100*i + j) + "  ") //循环嵌套    
//    println
//    for(i <- 1 to 2; j <- 1 to 2 if i != j) print((100*i + j) + "  ")
//    println 
//    
//    
//    def  addA(x : Int) = x +100
//    val  add = (x : Int) => x +200 //匿名函数
//    println("The result from a function is : " + addA(2))
//    println("The result from a val is : " + add(2))
//    def fac(n:Int):Int = if (n <= 0) 1 else n * fac(n - 1)
//    println("The result from a fac is : " + fac(10))
//    def combine(content:String, left: String = "[", right: String = "]") = left + content +right
//    println("The result from a combine is : " + combine("I love Spark", "<<"))
//    def connected(args: Int*) = {
//      var result =0
//      for(arg <- args) result += arg
//      result
//    }
//    println("The result from a connected is : " + connected(1,2,3,4,5,6))
//    
  }