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Exercise03.scala

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import java . awt . datatransfer . DataFlavor

import java . awt . datatransfer . SystemFlavorMap

import java . util . TimeZone

import scala . collection . mutable . ArrayBuffer

import scala . collection . mutable . Buffer

import scala . util . Random

/**

* 第三章的课后练习题

class Exercise03 {

/**

* (1) 将a设置为一个n个随机整数整数的数组,a介于 0~n之间

* val a = Array[Int](5) 这个表示是一个数组，里面只含有5这个元素。

* val a = new Array[Int](5) 这标示初始化一个5个元素的数组.

def randomAry ( n : Int ) : Array [ Int ] = {

val a = new Array [ Int ](n)

for (i < - 0 until n) {

a(i) = Random .nextInt(n)

}

/**

* (1)' 当然，还可以用ArrayBuffer

def randomAryBuffer ( n : Int ) : Array [ Int ] = {

val a = new ArrayBuffer [ Int ]()

for (i < - 0 until n) {

a + = Random .nextInt(n)

}

a.toArray

}

/**

* (2) 置换数组的元素

* scala> swapEle(Array[Int](1,2,3,4,5))

* res24: Array[Int] = Array(2, 1, 4, 3, 5)

def swapEle ( a : Array [ Int ]) : Array [ Int ] = {

val b = new ArrayBuffer [ Int ]()

// 0 until (a.length,2) 表示：

// 每2个元素一跳

// 从数组尾端开始则是:

// (0 until a.length).reverse

// P32

for (i < - 0 until (a.length, 2 )) {

if (i + 1 < a.length) {

b + = a(i + 1 )

b + = a(i)

} else {

b + = a(i)

}

b.toArray

}

/**

* (3) 第二题的for/yield版本

def swapEleForaYield ( a : Array [ Int ]) : Array [ Int ] = {

// 循环遍历a

val b = for (i < - 0 until a.length) yield {

if (i < a.length - 1 ) {

// 交换元素

if (i % 2 == 0 ) a(i + 1 ) else a(i - 1 )

} else {

a(i)

}

b.toArray

}

/**

* (4)过滤原来数组中的所有正数和负数

def filterArray ( a : Array [ Int ]) : Array [ Int ] = {

var b = a.filter { _ > 0 }

b ++ = a.filter { _ <= 0 }

b.toArray

}

/**

* (5) 计算数组的平均值

* average(Array[Double](12.34d,231d,1231.334d,-234.3d))

* res34: Double = 310.0935

def average ( a : Array [ Double ]) : Double = {

var sum = a.sum

sum / a.length

}

/**

* (6) 对于数组的反序

* var s=Array[Int](12,3,34,54,5)

* scala> s.reverse

* res36: Array[Int] = Array(5, 54, 34, 3, 12)

* ============================================

* var s=ArrayBuffer[Int](12,3,34,54,5)

* s: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(12, 3, 34, 54, 5)

* scala> s.reverse

* res37: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(5, 54, 34, 3, 12)

* 当然，还有排序过后的

* s.sorted.reverse

/**

* (7):去掉数组的重复值

* scala> s+=5

* res38: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(12, 3, 34, 54, 5, 5)

* scala> s.distinct

* res39: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(12, 3, 34, 54, 5)

def filterDuplicates ( a : Array [ Int ]) : Array [ Int ] = {

a.distinct

}

/**

* (8) 找到所有负数的下标，去掉最后一个的下标

def rewrite ( a : Array [ Int ]) : Array [ Int ] = {

val indexed = for (i < - 0 until a.length if a(i) < 0 ) yield i

a.dropRight(indexed.head)

}

/**

* (9)创建一个由java.util.TimeZone.gerAvailableIDs返回的集合,过滤掉美洲的

def filterTimeZone : Array [ String ] = {

val filterword = " America/ "

val a = TimeZone .getAvailableIDs()

// stripPrefix 返回去掉有指定前缀的字符串

/**

* scala> "Amer".stripPrefix("A")

* res48: java.lang.String = mer

a.filter(_.startsWith(filterword)).map(_.stripPrefix(filterword))

}

/**

* (10)

def flavors : Array [ String ] = {

import scala . collection . JavaConversions . _

import java . awt . datatransfer . DataFlavor

import java . awt . datatransfer . SystemFlavorMap

val command = ArrayBuffer ( " ls " , " -al " , " ~/bin " )

val pb = new java.lang. ProcessBuilder (command)

def flavors = SystemFlavorMap .getDefaultFlavorMap(). asInstanceOf [ SystemFlavorMap ]

var f : Buffer [ String ] = flavors.getNativesForFlavor( DataFlavor .imageFlavor)

f.toArray

}

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