Scala语法

常用语法：

package com.zscdmin
object demo1 {
    def main(args: Array[String]): Unit = {
        val a = List(1, 2, 3)
        val b = a.reduceLeft(_ + _)
        val c = a.reduceLeft((x, y) => x + y) //等价于上面的写法
        val d = a.foldRight(1)(_ * _)
        val e = a.foldLeft(0)(_ + _)
        println(b)
        println(c)
        println(d)
        println(e)
        val stream = 1 #:: 2 #:: 3 #:: Stream.empty
        println(stream(0)) //取第一个元素
        println(stream.apply(0)) //取第一个元素，【def apply(n: Int): A 通过列表中的索引选择一个元素】
        val l = 0 to 5
        println(l.map(x => x * x).zip(10 to 15))
        println(l.view.map(x => x * x).zip(10 to 15).force) //加上force强制求值,不加则暂时不求值
        val days = Array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")
        days.zipWithIndex.foreach { case (day, count) => println(s"$count is $day") }
        println("----------------")
        for ((day, count) <- days.zipWithIndex) {
            println(s"$count is $day")
        }
        println("----------------")
        for ((day, count) <- days.zip(Stream from 1)) {
            println(s"$count is $day")
        }
        val list1: List[Int] = List(1, 2, 3, 4)
        val list2: List[Int] = List(5, 6, 7, 8)
        val list3: List[Int] = List(2, 3, 4, 5, 6)
        val list4: List[Int] = List(7, 8, 9, 0, 3)
        var zip = list1.zip(list2)
        var zipAll = list1.zipAll(list2, "-2", "-1") //若列表长度不一致，对方列表较短的话使用thatElem进行填充
        var zipAll1 = list2.zipAll(list1, "-2", "-1") //若列表长度不一致，自身列表比较短的话使用thisElem进行填充
        println(zip) //zip函数将传进来的两个参数中相应位置上的元素组成一个pair数组。如果其中一个参数元素比较长，那么多余的参数会被删掉
        println(zipAll)
        println(zipAll1)
        //zipWithIndex函数可以将元素和其所在的下表组成一个pair
        var zipWithIndex = list1.zipWithIndex
        println(zipWithIndex)
        //unzip函数拆分元祖为List
        println(zip.unzip)
        var sort = List(10, 5, 8, 1, 7).sortWith(_ > _)
        println(sort)
        def sum(args: Int*) = {
            var result = 0
            for (arg <- args) result += arg
            result
        }
        println(sum(1 to 5: _*))
        val arr = Array(1, 2, 3, 4, 5)
        val Array(1, 2, _*) = arr
        val Array(first, second, _*) = arr
        println(first)
        println(second)
        val fun = 3 * (_: Double)
        println(fun(2))
        println(a.reduce(_ + _))
        println(a.map(_ + 2))
    }
}