3、数组和集合

数组

------------------------------------------------------------------

一维数组

object Demo2 {
  def main(args: Array[String]): Unit = {
    //定义数组，并指定长度
    val arr1 = new Array[Int](5)
    arr1(0) = 1
    arr1(2) = 4
    printarr(arr1)

    //初始化并赋值
    val arr2 = Array[String]("lyb","qqq")
    val arr22 = Array.apply[String]("lyb","qqq")
    val arr3 = Array("qq","ee")
    val arr33 = Array.apply("qq","ee")
  }

  def printarr(array: Array[Int]): Unit ={
    for(i <- 0 until array.length)print(array(i) + " ")
  }

}

多维数组

scala> val arr = Array.ofDim[String](2,3)
arr: Array[Array[String]] = Array(Array(null, null, null), Array(null, null, null))

scala> arr(0)(1)="qq"
scala> arr
res34: Array[Array[String]] = Array(Array(null, qq, null), Array(null, null, null))

数组缓冲区

----------------------------------------------------------------

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> val ab1 = new ArrayBuffer[Int](5)
ab1: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()

append

scala> ab1.append
   def append(elems: Int*): Unit

scala> ab1.append(1,2,3)

scala> ab1
res1: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3)

prepend

scala> ab1.prepend
   def prepend(elems: Int*): Unit

scala> ab1.prepend(4,5)

scala> ab1
res3: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(4, 5, 1, 2, 3)

length

scala> ab1.length
res5: Int = 5

+=　　修改自身

scala> ab1 += 6
res6: ab1.type = ArrayBuffer(4, 5, 1, 2, 3, 6)

.++=　　修改自身

scala> ab1.++= (7 to 8)
res7: ab1.type = ArrayBuffer(4, 5, 1, 2, 3, 6, 7, 8)

-=　　删除前面的值

scala> ab1
res13: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(4, 5, 1, 2, 3, 6, 7, 8, 7, 8)

scala> ab1.-=8
<console>:1: error: ';' expected but integer literal found.
ab1.-=8
      ^

scala> ab1.-=(8)
res14: ab1.type = ArrayBuffer(4, 5, 1, 2, 3, 6, 7, 7, 8)

trimEnd

scala> ab1.trimEnd
   def trimEnd(n: Int): Unit

scala> ab1.trimEnd(3)

scala> ab1
res16: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(4, 5, 1, 2, 3, 6)

insert

scala> ab1.insert
   def insert(n: Int,elems: Int*): Unit

scala> ab1.insert(1,0 to 3:_*)

scala> ab1
res18: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(4, 0, 1, 2, 3, 5, 1, 2, 3, 6)

toArray

scala> ab1.toArray
   def toArray[B >: Int](implicit evidence$1: scala.reflect.ClassTag[B]): Array[B]

scala> ab1.toArray
res19: Array[Int] = Array(4, 0, 1, 2, 3, 5, 1, 2, 3, 6)

 reverse

scala> ab1
res23: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(4, 0, 1, 2, 3, 5, 1, 2, 3, 6)

scala> ab1.reverse
res24: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(6, 3, 2, 1, 5, 3, 2, 1, 0, 4)

scala> ab1
res25: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(4, 0, 1, 2, 3, 5, 1, 2, 3, 6)

sum、max...

scala> ab1.sum
res26: Int = 27

scala> ab1.max
res27: Int = 6

mkString

scala> ab1.mkString
                       def mkString(sep: String): String
def mkString: String   def mkString(start: String,sep: String,end: String): String

scala> ab1.mkString(",")
res30: String = 4,0,5,1,2,3

java和scala互操作

--------------------------------------------------------------------------------

1、java的List 转 scala的Buffer

scala> val list:java.util.List[String] = new java.util.ArrayList()
list: java.util.List[String] = []

scala> list.add("qq")
res27: Boolean = true

scala> list.add("ww")
res28: Boolean = true

scala> list
res29: java.util.List[String] = [qq, ww]

scala> import scala.collection.JavaConversions.asScalaBuffer
import scala.collection.JavaConversions.asScalaBuffer

scala> val buff = list.toBuffer
buff: scala.collection.mutable.Buffer[String] = ArrayBuffer(qq, ww)

scala> buff
res30: scala.collection.mutable.Buffer[String] = ArrayBuffer(qq, ww)

2、scala的Buffer 转 java的List

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> val arr = ArrayBuffer("qq","ww")
arr: scala.collection.mutable.ArrayBuffer[String] = ArrayBuffer(qq, ww)

scala> import scala.collection.JavaConverters.bufferAsJavaListConverter
import scala.collection.JavaConverters.bufferAsJavaListConverter

scala> arr.asJava
res0: java.util.List[String] = [qq, ww]