1 // 对Array进行转换，获取的还是Array
 2 val a = Array(1, 2, 3, 4, 5)
 3 val a2 = for (ele <- a) yield ele * ele
 4 // 对ArrayBuffer进行转换，获取的还是ArrayBuffer
 5 val b = ArrayBuffer[Int]()
 6 b += (1, 2, 3, 4, 5)
 7 val b2 = for (ele <- b) yield ele * ele
 8 // 结合if守卫，仅转换需要的元素
 9 val a3 = for (ele <- if ele % 2 == 0) yield ele * ele
10 
11 // 使用函数式编程转换数组（通常使用第一种方式）
12 a.filter(_ % 2 == 0).map(2 * _)
13 a.filter { _ % 2 == 0 } map { 2 * _ }

 1 // 构建数组
 2 val a = ArrayBuffer[Int]()
 3 a += (1, 2, 3, 4, 5, -1, -3, -5, -9)
 4 
 5 // 每发现一个第一个负数之后的负数，就进行移除，性能较差，多次移动数组
 6 var foundFirstNegative = false
 7 var arrayLength = a.length
 8 var index = 0
 9 while (index < arrayLength) {
10   if (a(index) >= 0) {
11     index += 1
12   } else {
13     if (!foundFirstNegative) { foundFirstNegative = true; index += 1 }
14     else { a.remove(index); arrayLength -= 1 }
15   }
16 } 

 1 // 重新构建数组
 2 val a = ArrayBuffer[Int]()
 3 a += (1, 2, 3, 4, 5, -1, -3, -5, -9)
 4 
 5 // 每记录所有不需要移除的元素的索引，稍后一次性移除所有需要移除的元素
 6 // 性能较高，数组内的元素迁移只要执行一次即可
 7 var foundFirstNegative = false
 8 val keepIndexes = for (i <- 0 until a.length if !foundFirstNegative || a(i) >= 0) yield {
 9   if (a(i) < 0) foundFirstNegative = true
10   i
11 }
12 for (i <- 0 until keepIndexes.length) { a(i) = a(keepIndexes(i)) }
13 a.trimEnd(a.length - keepIndexes.length)