Scala初探（二）

5. 单例模式

class Marker(val color: String){
	//类中的任何代码段作为构造函数的一部分
	println("Creating " + this)

	override def toString(): String = "marker color " + color 
}

object MarkerFactory{
	private val markers = Map(
		"red" -> new Marker("red"),
		"blue" -> new Marker("blue"),
		"green" -> new Marker("green")
		)

	def getMarker(color:String) = if(markers.contains(color)) markers(color) else null	
}

println(MarkerFactory getMarker "blue")
println(MarkerFactory.getMarker("blue"))

6. 独立对象和伴生对象

//marker的构造函数标记为private，但是伴生对象依然可以访问它
//在marker类或伴生对象之外创建marker实例，就会得到错误信息
class Marker private(val color: String){
	println("Creating " + color)

	override def toString(): String = "marker color " + color
}
//伴生对象
object Marker{
	private val markers = Map(
		"red" -> new Marker("red"),
		"blue" -> new Marker("blue"),
		"green" -> new Marker("green")
		)

	def getMarker(color: String) = if(markers.contains(color)) markers(color) else null
}

println(Marker getMarker "red")
println(Marker getMarker "bule")
println(Marker getMarker "blue")

7. 容器

//容器
import java.util._

var list1: List[Int] = new ArrayList[Int]

list1 add 1
list1 add 2

var total = 0
for(i <- 0 until list1.size()){
	total += list1.get(i)
}


println("The total is " + total)

def totalResultOverRange(number: Int,codeBlock: Int => Int): Int = {
	var result = 0
	for(i <- 1 to number){
		result += codeBlock(i)
	}

	result
}

println(totalResultOverRange(11,i => i))
println(totalResultOverRange(11,i => if(i%2 == 0) 1 else 0))

9.  具有多参数的高阶函数

def inject(arr: Array[Int],initial:Int,operation: (Int,Int) => Int): Int = {
	var carryover = initial
	arr.foreach(element => carryover = operation(carryover,element))

	carryover
}

val array = Array(2,3,5,1,6,4)
val sum = inject(array,0,(carryOver,elem) => carryOver + elem)

println("Sum of elements in array is " + sum)

val max = inject(array,0,(carryOver,elem) => Math.max(carryOver,elem))
println("Max of the array is " + max)

val array = Array(2,3,5,1,6,4)

val sum = (0 /: array){
	(sum,elem) => sum + elem
}

val max = (Integer.MIN_VALUE /: array){
	(large,elem) => Math.max(large,elem)
}

println("Sum of elements in array is " + sum)
println("Max of elements in array is " + max)

Scala初探（二）