快学scala之数组操作

最新推荐文章于 2024-06-15 01:14:41 发布

u014372225

最新推荐文章于 2024-06-15 01:14:41 发布

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分类专栏： scala

本文链接：https://blog.youkuaiyun.com/u014372225/article/details/75094666

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这篇博客介绍了Scala中数组和ArrayBuffer的操作，包括初始化、遍历、获取元素、使用foreach、过滤、映射以及求和等方法。还展示了如何在ArrayBuffer与数组间转换，并提供了mkString和自定义字符串拼接的例子。

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object Array_opt {

  def main(args: Array[String]) {

    // init an array
    val array = new Array[String](3)
    val arr = Array(1, 2, 3, 4)

    // traversal element
    // method 1
    for (i <- 0 until arr.length) {
      print(arr(i))
    }
    // method 2
    for (ele <- arr) {
      println(ele)
    }
    // method 3
    for (i <- 0 to arr.length - 1) println(arr(i))
    // get element use () replace []
    println(arr(0))
    // method 4:use foreach
    arr.foreach(println)
    // use exp: for(ele <- arr if(exp)) yield change to a new array
    val newArr = for (ele <- arr if ele % 2 == 0) yield ele
    newArr.foreach(println)

    // ------------  buffered array -----------------------
    val buf = ArrayBuffer[Int]()
    // add element
    buf += 1
    // add an array
    buf +=(2, 3)
    println(buf.getClass) //class scala.collection.mutable.ArrayBuffer
    buf ++= Array(4, 5, 6)
    for (value <- buf) {
      if (value >= 3) println(value)
    }
    // change into array
    buf.toArray
    // array change into ArrayBuffer
    arr.toBuffer

    // filter map
    //def filter(p: A => Boolean): (apply every element in array)
    buf.filter(_ % 2 == 0).map(_ * 2).foreach(println)
    for (ele <- buf if ele % 2 == 0) yield ele * 2
    // get sum
    println(buf.sum)
    println(Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).sum) //55

    println(buf.mkString("-"))
    // start , separate ,end
    println(buf.mkString("<", ",", ">")) //<1,2,3,4,5,6>

    for (i <- 1 to 2; j <- 1 to 2 if (i != j)) println(i * 10 + j)

    def fac(n: Int): Int = if (n <= 0) 1 else n * fac(n - 1)
    println(fac(3))

    def makeString(s: String, left: String = "[", right: String = "]") = left + s + right

  }
}