Scala学习笔记（四）—— 数组

定长数组Array

定义定长数组用Array，有如下几种方法：

  • 初始化一个长度为8的定长数组，其所有元素默认值均为0 
    1 scala> new Array[Int](8)
2 res0: Array[Int] = Array(0, 0, 0, 0, 0, 0, 0, 0)
  • 调用静态方法，直接为数组赋值 
     1 scala> val arr2 = Array[Int](8)
 2 arr2: Array[Int] = Array(8)
 3 
 4 scala> arr2.length
 5 res16: Int = 1
 6 
 7 scala> Array(1,"1")
 8 res17: Array[Any] = Array(1, 1)
 9 
10 scala> val arr3 = Array(1,"string",3.14)
11 arr3: Array[Any] = Array(1, string, 3.14)
12 
13 scala> val arr4 = Array(1,2,3)
14 arr4: Array[Int] = Array(1, 2, 3)

     

变长数组ArrayBuffer

  • 需要导入import scala.collection.mutable.ArrayBuffer包 
    1 scala> import scala.collection.mutable.ArrayBuffer
2 import scala.collection.mutable.ArrayBuffer

     

  • 初始化有以下两种方法： 
    1 scala> import scala.collection.mutable.ArrayBuffer
2 import scala.collection.mutable.ArrayBuffer
3 
4 scala> val ab =new ArrayBuffer[Int]()
5 ab: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
6 
7 scala> val ab1 = ArrayBuffer(1,2)
8 ab1: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2)

     

  • 使用+=追加（多个）元素，使用++= 追加数组 
     1 scala> ab += 1
 2 res0: ab.type = ArrayBuffer(1)
 3 
 4 scala> ab += 2
 5 res1: ab.type = ArrayBuffer(1, 2)
 6 
 7 scala> ab += (3,4,5)
 8 res2: ab.type = ArrayBuffer(1, 2, 3, 4, 5)
 9 
10 scala> ab ++= Array(6,7)
11 res4: ab.type = ArrayBuffer(1, 2, 3, 4, 5, 6, 7)
12 
13 scala> ab ++= ArrayBuffer(8,9)
14 res5: ab.type = ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8, 9)

     

  • 指定位置插入元素：第一个入参是指定要插入的下标，后面的元素则插入在该下标及其之后 
     1  scala> ab
 2  res0: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 6,7, 8, 9)
 3  
 4  scala> ab.insert(0,0)
 5  
 6  scala> ab
 7  res2: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
 8  
 9  scala> ab.length
10  res3: Int = 10
11   
12  scala> ab.insert(11,11)
13  java.lang.IndexOutOfBoundsException: 11
14    at scala.collection.mutable.ArrayBuffer.insertAll(ArrayBuffer.scala:139)
15    at scala.collection.mutable.BufferLike$class.insert(BufferLike.scala:167)
16    at scala.collection.mutable.AbstractBuffer.insert(Buffer.scala:49)
17    ... 32 elided
18  
19  scala> ab.insert(10,10)
20  
21  scala> ab
22  res7: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

      注意：插入的下标 <= 该数组的长度，若插入的下标为数组的长度则表示在末尾追加；若插入的下标大于该数组的长度，则报错数组越界 IndexOutOfBoundsException

 

  • 删除指定位置的元素：第一个入参是指定要删除的下标；第二个入参是要删除的数据的长度，默认值为1 
     1 scala> ab.length
 2 res9: Int = 11
 3 
 4 scala> ab.remove(11)
 5 java.lang.IndexOutOfBoundsException: 11
 6   at scala.collection.mutable.ResizableArray$class.apply(ResizableArray.scala:43
 7 )
 8   at scala.collection.mutable.ArrayBuffer.apply(ArrayBuffer.scala:48)
 9   at scala.collection.mutable.ArrayBuffer.remove(ArrayBuffer.scala:169)
10   ... 32 elided
11 
12 scala> ab.remove(10)
13 res11: Int = 10
14 
15 scala> ab
16 res12: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
17 
18 scala> ab.remove(9,2)
19 java.lang.IndexOutOfBoundsException: 9
20   at scala.collection.mutable.ArrayBuffer.remove(ArrayBuffer.scala:158)
21   ... 32 elided
22 
23 scala> ab.length
24 res14: Int = 10
25 
26 scala> ab.remove(9,1)
27 
28 scala> ab
29 res16: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8)

　　　　注意：要删除的下标 < 数组的长度， 否则报错数组越界 IndexOutOfBoundsException

 

  • 遍历数组

　　　　请参考笔记（二）for循环

 

  • 数组常用算法

    　用filter方法进行过滤

    scala> ab
res22: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 6, 7, 8)

scala> ab.filter(_ % 2 == 0)
res23: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 2, 4, 6, 8)

      用map方法进行数组转换

    1 scala> ab
2 res24: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8)
3 
4 scala> ab.map(_ * 10)
5 res25: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 10, 20, 30, 40, 50, 60, 70, 80)

     例：将数组中偶数取出来乘以100

    1 scala> ab
2 res26: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8)
3 
4 scala> ab.filter(_ % 2 == 0).map(_*100)
5 res27: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 200, 400, 600, 800)

     数组求和、最小值、最大值、排序

    scala> ab
res35: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 10, 50, 30, 5, 6, 7, 8)

scala> ab.sum
res36: Int = 126

scala> ab.min
res38: Int = 0

scala> ab.max
res39: Int = 50

scala> ab.sorted
res40: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 30, 50)

     

 

posted @ 2018-10-28 16:17  LALALA823  阅读(401)  评论(0)  编辑  收藏  举报