Scala中可变数组和不可变数组的创建和访问

package com.atguigu.scala.chapter07

import scala.collection.mutable.ArrayBuffer

/**
 * @author yymstart
 * @create 2020-09-16 16:33
 */


//可变数组
object Test02_ArrayBuffer {

  def main(args: Array[String]): Unit = {
    //创建可变数组
    //可以不传参数，默认16
    var arr1:ArrayBuffer[Int] = new ArrayBuffer[Int]()
    val arr2 = ArrayBuffer(2,3,4)

    //array必须mkstring，这个不用，因为底层又索引
    println(arr1) //ArrayBuffer()
    println(arr2) //ArrayBuffer(2, 3, 4)

    //2.fangwen数组元素进行读写操作
    //直接访问角标越界
    println(arr2(2))//4
    //运行报错，需要使用添加方法
    //arr1(0) = 12
    //底层同样是update方法
    arr2(0) = 12
    println(arr2)//ArrayBuffer(12, 3, 4)

    println("=====================")
    //3.向数组中添加元素，可变集合不推荐
    arr1 :+ 200
    //ArrayBuffer()，底层b ++= thisCollection
    println(arr1)//ArrayBuffer()

    //强行使用,不推荐
    val newArr1 = arr1 :+ 200

    //最好使用的是英文表示
    arr1.append(1,2,2,2,2,3)
    println(arr1)//ArrayBuffer(1, 2, 2, 2, 2, 3)

    //往前加
    arr1.prepend(0)
    println(arr1)//ArrayBuffer(0, 1, 2, 2, 2, 2, 3)

    //往任意位置添加
    arr1.insert(1,100000000,200000000)
    println(arr1)//ArrayBuffer(0, 100000000, 200000000, 1, 2, 2, 2, 2, 3)

    //符号方法的调用
    println("符号方法的调用")
    println(arr2)//ArrayBuffer(12, 3, 4)
    arr2 += 23
    println(arr2)//ArrayBuffer(12, 3, 4, 23)

    10 +=: arr2
    println(arr2)//ArrayBuffer(10, 12, 3, 4, 23)


    //4.删除元素,按照索引删除
    val a = arr2.remove(2)  //按索引位置删除
    arr2.remove(2,2)
    println(arr2)//ArrayBuffer(10, 12)
    println(a)//3

    //符号的删除方法，按值删除
    arr2 -= 2
    println(arr2)//ArrayBuffer(10, 12)

    //5.增加另一个数组的所有元素
    arr2.appendAll( ArrayBuffer(27,47,80) )
    println(arr2)//ArrayBuffer(10, 12, 27, 47, 80)
    //谁调用便用谁
    arr2++=arr1
    println(arr2)//ArrayBuffer(10, 12, 27, 47, 80, 0, 100000000, 200000000, 1, 2, 2, 2, 2, 3)

    arr2 ++=: arr1
    println(arr1)//ArrayBuffer(10, 12, 27, 47, 80, 0, 100000000, 200000000, 1, 2, 2, 2, 2, 3, 0, 100000000, 200000000, 1, 2, 2, 2, 2, 3)

    //6.还可以做一个可变数组和不可变数组的转换
    val arr:ArrayBuffer[Int] = ArrayBuffer(2,4,7)
    val newArr:Array[Int] = arr.toArray
    println(newArr)  //[[email protected]
    println(newArr.mkString("-"))//2-4-7
    println(arr)//ArrayBuffer(2, 4, 7)

    val buffer = newArr.toBuffer
    println(buffer)//ArrayBuffer(2, 4, 7)
    println(newArr) //[[email protected]
    println(newArr.mkString(" "))//2 4 7
  }
}

---

不可变数组

package com.atguigu.scala.chapter07

/**
 * @author yymstart
 * @create 2020-09-16 15:25
 */
object Test01_Array {
  def main(args: Array[String]): Unit = {
    //1.创建一个不可变数组
    //1.new
    val arr1:Array[Int] = new Array[Int](5)
    //2.用半生对象的apply方法
    val arr2 :Array[Int] = Array(1,2,3,4,5)
    println("===================")

    //2.访问数组中元素，做读写操作.这里的apply是array的方法
    println(s"${arr1(0)} ${arr1(1)} ${arr1.apply(2)} ${arr1(3)} ${arr1(4)} ")

    //不可变是不能该长度，内容可以改
    //底层还是一个方法
    arr1(3) = 100000000
    arr1.update(4,20000000)
    arr1(2) = 270000000

    //array继承的是Java的序列化，打印的是地址
    println(arr1)

    println(arr1.mkString("-"))


    //3.遍历所有元素
    //1.for循环,遍历索引
    for ( i <- 0 until arr2.length )
      println(arr2(i) + "\t")

    println()

    for ( i <- arr2.indices )
      println(arr2(i) + "\t")
    println()

    //2.for循环直接遍历元素
    for (elem <- arr2) print(elem +"\t")

    println()

    //3.迭代器  下面的虚线全是隐式转换
    var iter:Iterator[Int] = arr2.iterator
    while(iter.hasNext){
      print(iter.next() + "\t")
    }
    println()

    //4.foreach方法
    arr2.foreach(elem=>print(elem + "\t"))
    println()

    arr2.foreach(println(_))


    //4.向数组中添加元素
    //生成一个新的数组，原数组不变
    val newArr1:Array[Int] = arr2.:+(20)
    println(arr2.mkString(" "))
    println(newArr1.mkString(" "))

    val newArr2:Array[Int] = arr2.+:(0)
    println(newArr2.mkString(" "))

    val newArr3 = arr1 :+ 39

    //:在后面的话是从右往左调用
    //val newArr3 = arr1 +: 15
    val newArr4 = 15 +: arr1
  }

}