2. scala中的数组

一. 数组声明

1. 定长数组

   scala> new Array[String](5)
   res1: Array[String] = Array(null, null, null, null, null)
   
   scala> Array("a","b",1)
   res4: Array[Any] = Array(a, b, 1)
   

2. ArrayBuffer

   scala> import scala.collection.mutable.ArrayBuffer
   import scala.collection.mutable.ArrayBuffer
   
   scala> b += 11
   res0: b.type = ArrayBuffer(11)
   
   scala> val arr2 = Array(22,23)
   arr2: Array[Int] = Array(22, 23)
   
   scala> b ++= arr2
   res1: b.type = ArrayBuffer(11, 22, 23)
   
   scala> b.insert(1,0)
   scala> b
   res4: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(11, 0, 22, 23)
   
   scala> b.remove(2)
   scala> b
   res6: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(11, 0, 23)
   
   

二. 数组的操作

1. 遍历

   //正序遍历
   scala> 0 until b.length
   res7: scala.collection.immutable.Range = Range(0, 1, 2)
   scala> for(i <- 0 until b.length) print(b(i)+",")
   11,0,23,
   
   //逆序遍历
   scala> (0 until b.length).reverse
   res10: scala.collection.immutable.Range = Range(2, 1, 0)
   scala> for(i <- (0 until b.length).reverse) print(b(i)+",")
   23,0,11,
   
   //简单遍历
   scala> for(i <- b) print(i+",")
   11,0,23,
   

2. filter，map与yield，守卫
   
   for循环中使用守卫过滤元素，用yield产生集合的效果和对数组对象使用filter再使用map的效果相同

   scala> for(i <- b if i%2==1) yiel
   d i*2
   res17: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(22, 46)
   
   scala> b.filter(_%2 == 1).map(_*2)
   res15: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(22, 46)
   

3. sum,max,sortWith,mkString

   scala> val arr = Array(1,2,3)
   arr: Array[Int] = Array(1, 2, 3)
   
   scala> arr.sum
   res28: Int = 6
   
   scala> arr.max
   res29: Int = 3
   
   scala> arr.sortWith(_>_)
   res38: Array[Int] = Array(3, 2, 1)
   
   // Array用mkString显示内容好，ArrayBuffer使用toString显式好
   scala> arr.mkString(",")
   res39: String = 1,2,3
   
   scala> arr.toString
   res40: String = [I@22ab5262
   
   scala> buffer.mkString(",")
   res41: String = 11,34,23
   
   scala> buffer.toString
   res42: String = ArrayBuffer(11, 34, 23)   //带变量类型
   
   

4. 多维数组

   //规则的多维数组
   scala> Array.ofDim[Int](2,2)
   res46: Array[Array[Int]] = Array(Array(0, 0), Array(0, 0))
   
   //不规则的多维数组
   
   

5. scala的ArrayBuffer和java的ArrayList转换

   import java.io.{BufferedReader, InputStreamReader}
   
   import scala.collection.mutable.ArrayBuffer
   import scala.collection.JavaConversions.bufferAsJavaList    //隐士转换
   
   val cmd = ArrayBuffer("ls","-al","/home/lj")
   val builder: ProcessBuilder = new ProcessBuilder(cmd)  //ProcessBuilder接受ArrayList，隐士转换后可接受ArrayBuffer
   val process: Process = builder.start()
   val reader: BufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream))
   var str = "";
   while((str=reader.readLine())!=null)
     println(str)