scala中ArrayBuffer簡單使用

import scala.collection.mutable.ArrayBuffer

/**
  * 與Array區別：
  * 1、Array是不可變的，不能直接地對其元素進行刪除操作，只能通過重賦值或過濾生成新的Array的方式來刪除不要的元素
  * 2、ArrayBuffer是可變的，提供了很多元素的操作，包括刪除的操作
  * 他們相互轉化很方便，調用toArray 、toBuffer方法即可
  */
object ArrayBufferUse {

  def main(args: Array[String]): Unit = {

    val b = ArrayBuffer[Int]()
    b+= 1;
    b+= (2,3,4,5,6)
    b.remove(1) // 刪除元素
    println(b.mkString(","))


    // 變成Array
    val ary = b.toArray
    println(ary.mkString(","))

    println(ary.sum)
    println(ary.max)
    println(ary.min)
    println(ary.toBuffer.toString)

    // yield
    var b1 = for(ele <- ary) yield ele * ele
    println(b1.mkString(","))

    val ab = ArrayBuffer[Int]()
    ab +=(2,3,4,5,6)

    val c = for(ele <- ab) yield ele * ele
    println(c.mkString(","))

    // 找出來偶數
    val d1 = for(ele <- ab if ele % 2 == 0) yield ele * ele
    println(d1.mkString(","))

    // 函數式編程 _ 表示元素
    println(d1.filter(_ % 2 == 0).map(_ * 3).mkString(","))

    removeNegativeBad()

    removeNegativeGood()

  }

  def removeNegativeBad()={
    val ab = new ArrayBuffer[Int]()
    ab += (1,2,3,4,5,-1,-2,-3)

    var findNegative = false
    var index = 0
    var abLen =ab.length
    while (index < abLen) {
      if(ab(index) >=0 ){
        index += 1
      }else{
        if(!findNegative){
          findNegative = true;
          index+=1
        }else{
          ab.remove(index)
          abLen -=1
        }
      }
    }
    println(ab.mkString(","))
  }

  def removeNegativeGood()={
    val ab = ArrayBuffer[Int]()
    ab+=(1,2,3,4,-1,-2,-3,-4,-5)
    var foundNegative = false
    val keepIndex = for (i <- 0 until ab.length if !foundNegative || ab(i) >= 0) yield {
      if(ab(i) < 0 ) foundNegative = true
      i
    }
    for (i <- 0 until keepIndex.length){
      ab(i) = ab(keepIndex(i))
    }
    ab.trimEnd(ab.length - keepIndex.length)
    println(ab)
  }

}