Scala集合

1. 数组

1.1 定长数组Array

/**
 * Author: 3zZ.
 * Date: 2020/1/8 7:56 下午
 */
object ArrayApp extends App {
  val a = new Array[String](5) // Array(null,...null)
  a.length // 5
  a(1) = "hello"
  a(1) // String = "hello"
  val b = Array("hadoop", "spark", "storm")
  b(1) = "flink"
  b // Array(hadoop, flink, storm)
  val c = Array(2,3,4,5,6,7,8,9)
  c.sum // Int = 44
  c.min // Int = 9
  c.max // Int = 2
  c.mkString // String = 23456789
  c.mkString(",") //String = 2,3,4,5,6,7,8,9
  c.mkString("<",",",">") // String = <2,3,4,5,6,7,8,9>
  c.toString // String = [I@44e3760b
}

1.2 变长数组ArrayBuffer

/**
 * Author: 3zZ.
 * Date: 2020/1/8 7:56 下午
 */
object ArrayApp extends App {
  val c = scala.collection.mutable.ArrayBuffer[Int]()
  c += 1 // ArrayBuffer(1)
  c += (2,3,4,5) // ArrayBuffer(1, 2, 3, 4, 5)
  c ++= Array(6,7,8) // ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8)
  c.insert(0,0) // ArrayBuffer(0, 1, 2, 3, 4, 5, 6, 7, 8)
  c.remove(1) // ArrayBuffer(0, 2, 3, 4, 5, 6, 7, 8)
  c.remove(0,3) // ArrayBuffer(4, 5, 6, 7, 8)
  c.trimEnd(2) // ArrayBuffer(4, 5, 6)
  c.toArray.mkString // 456(Array类型)
  for(ele <- c){
    println(ele) // 遍历 4 5 6
  }
  for(i <- (0 until c.length).reverse) {
    println(c(i)) // 逆序 6 5 4
  }
}

2. List

• 有序的
• 可以重复的

2.1 Nil是什么

scala> Nil
scala.collection.immutable.Nil.type = List()

• Nil就是一个空的List

2.2 List使用

/**
 * Author: 3zZ.
 * Date: 2020/1/9 4:57 下午
 */
object ListApp extends App {
  val l = List(1,2,3,4,5) // l: List[Int] = List(1, 2, 3, 4, 5)
  l.head // Int = 1
  l.tail // List[Int] = List(2, 3, 4, 5)
  val l2 = 1 :: Nil // l2: List[Int] = List(1)
  val l3 = 2 :: l2 //  l3: List[Int] = List(2, 1)
  val l4 = 1 :: 2 :: 3 :: Nil // l4: List[Int] = List(1, 2, 3)
  val l5 = scala.collection.mutable.ListBuffer[Int]()
  l5 +=  2 // ListBuffer(2)
  l5 += (3,4,5) // ListBuffer(2, 3, 4, 5)
  l5 ++= List(6,7,8) // ListBuffer(2, 3, 4, 5, 6, 7, 8)
  l5 -= 2 // ListBuffer(3, 4, 5, 6, 7, 8)
  l5 -= (1,4) // ListBuffer(2, 3, 5, 6, 7, 8)
  l5 --= List(2,3,5,6) // ListBuffer(7, 8)
  l5.toList // List[Int] = List(7, 8)
  l5.toArray // Array[Int] = Array(1, 3, 4, 5)
  l5.head // Int = 1
  l5.isEmpty // Boolean = false
  l5.tail // scala.collection.mutable.ListBuffer[Int] = ListBuffer(3, 4, 5)
  l5.tail.head // Int = 3
  
  def sum(nums:Int*):Int = {
    if(nums.length == 0){
      0
    } else{
      nums.head + sum(nums.tail:_*) // 自动把Seq转换为Int*
    }
  }
  sum(1,2,3,4) // Int = 10
}

3. Set

• 无序的
• 不可重复的

/**
 * Author: 3zZ.
 * Date: 2020/1/9 6:24 下午
 */
object SetApp extends App{
  val set = scala.collection.mutable.Set[Int]()
  set += 1 // set.type = Set(1)
  set += (2,1) // set.type = Set(1,2)
}

• 其他用法基本与List相同

4. Map

5. Option & Some & None

6. Tuple