//1.定长数组
    val arr1 = new Array[Int](10) //不定义[Int] 默认为 [Nothing]
    println(arr1.mkString(","))

    val arr2 = Array(1, 2, 3)
    println(arr2.mkString(","))
    arr2.apply(1)

    //赋值
    arr2(1) = 10 //等价于 arr2.update(1, 10)
    println(arr2.mkString(","))

    //追加
    val arr3 = arr1 :+ "??"
    val arr4 = "??" :+ arr1
    println(arr3.mkString(", "))

    //2.变长数组
    //小括号可以存放初始化的元素内容
    val arrBuffer1 = ArrayBuffer[Int](10, 9, 8)
    val arrBuffer2 = ArrayBuffer[Int]() //小括号中指定的元素
    println(arrBuffer1) //ArrayBuffer(10, 9, 8) 直接打印的是数组
    println(arrBuffer2) //ArrayBuffer()
    println(arrBuffer1.mkString(",")) //10,9,8

    //赋值，取值
    arrBuffer1(1) = -1
    println(arrBuffer1) //ArrayBuffer(10, -1, 8)
    println(arrBuffer1(1)) //-1
    println(arrBuffer1.apply(2)) //8

    //追加
    arrBuffer1.append(1, 2, 3)
    println(arrBuffer1) //ArrayBuffer(10, -1, 8, 1, 2, 3)

    val arrBuffer3 = arrBuffer1 :+ 90
    println(arrBuffer1) //ArrayBuffer(10, -1, 8, 1, 2, 3)
    println(arrBuffer3) //ArrayBuffer(10, -1, 8, 1, 2, 3, 90)

for (i <- 0 until a.length)
    println(i + ": " + a(i))

for (elem <- a)
    println(elem)