數組常用方法 · JAVA

[TOC] # 定義 ~~~ //初始化一個長度為8的定長數組,其所有元素均為0 val arr1 = new Array[Int](8) //直接打印定長數組,內容為數組的hashcode值 println(arr1) //將數組轉換為數組緩沖,就可以看到原數組的內容了 //toBuffer會將數組轉換為長數組緩沖 println(arr1.toBuffer) //注意: 如果new,相當于調用了數組的apply方法,直接為數組賦值 //初始化一個長度為1的定長數組 val arr2 = Array[Int](10) println(arr1.toBuffer) //定義一個長度為3的定長數組 val arr3 = Array("hadoop", "storm", "spark") //使用()來訪問元素 println(arr3(2)) ~~~ # 賦值及取值 ~~~ //等價于 arr2(1)=10 scala> arr2.update(1,10) scala> arr2 res6: Array[Int] = Array(1, 10, 3) ~~~ 也可以通過apply來取值 ~~~ scala> arr2.apply(1) res9: Int = 10 ~~~ # 變長數組需要打包 ~~~ # _表示導入這個包下的所有 scala> import scala.collection.mutable._ import scala.collection.mutable._ scala> val ab = new ArrayBuffer[Int]() ab: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer() scala> val arrBuffer1 = scala.collection.mutable.ArrayBuffer[Int](10,9,8) arrBuffer1: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(10, 9, 8) ~~~ ## 追加元素 ~~~ # 向尾部追加 scala> ab += 1 res0: ab.type = ArrayBuffer(1) scala> ab += (3, 4, 5) res1: ab.type = ArrayBuffer(1, 3, 4, 5) # 追加一個數組緩沖 scala> ab ++= Array(6, 7) res2: ab.type = ArrayBuffer(1, 3, 4, 5, 6, 7) # 追加一個數組緩沖 scala> ab ++= ArrayBuffer(8, 9) res3: ab.type = ArrayBuffer(1, 3, 4, 5, 6, 7, 8, 9) # 向尾部追加 ab.append(123) ~~~ 指定位置插入用insert ~~~ # 在0這個位置插入-1和0 ab.insert(0, -1, 0) ~~~ 會生成一個新的數組 ~~~ scala> ab :+ 99 res14: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(123, 3, 99) scala> ab res15: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(123, 3) ~~~ ## 刪除 ~~~ scala> ab res5: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(-1, 0, 1, 3, 4, 5, 6, 7, 8, 9) # 刪除數組某個位置的元素 # 在3這個位置移除2個 scala> ab.remove(3, 2) scala> ab res7: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(-1, 0, 1, 5, 6, 7, 8, 9) ~~~ ## 定長數組和變長數組的轉換 ~~~ scala> arr2.toBuffer res7: scala.collection.mutable.Buffer[Int] = ArrayBuffer(1, 10, 3) scala> arr2.toArray res8: Array[Int] = Array(1, 10, 3) ~~~ # 排序 ~~~ scala> val arr = Array(1, 9, 5, 7, 3, 2) arr: Array[Int] = Array(1, 9, 5, 7, 3, 2) ~~~ **升序** ~~~ scala>arr.sorted res0: Array[Int] = Array(1, 2, 3, 5, 7, 9) ~~~ **降序** ~~~ scala> arr.sorted.reverse res2: Array[Int] = Array(9, 7, 5, 3, 2, 1) ~~~ ~~~ scala> arr.sortWith(_>_) res1: Array[Int] = Array(9, 7, 5, 3, 2, 1) ~~~ 也可以這樣寫 ~~~ scala> arr.sortWith( (x, y) => x > y ) res3: Array[Int] = Array(9, 7, 5, 3, 2, 1) ~~~ **轉換后排序** ~~~ scala> val arr = Array(1,2,3,4,10,100) arr: Array[Int] = Array(1, 2, 3, 4, 10, 100) scala> arr.sortBy(x => x+"") res0: Array[Int] = Array(1, 10, 100, 2, 3, 4) ~~~ # 數組轉換 yield關鍵字將原始的數組進行轉換會產生一個新的數組,原始的數組不變 ~~~ scala> var arr = Array(1, 2, 3, 4, 5, 6, 7) arr: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7) scala> val res = for(e <- arr) yield e*2 res: Array[Int] = Array(2, 4, 6, 8, 10, 12, 14) scala> arr.map(_ * 2) res0: Array[Int] = Array(2, 4, 6, 8, 10, 12, 14) scala> arr res1: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7) ~~~ # 過濾偶數乘以10 ~~~ scala> arr.filter(_ % 2 == 0).map(_ * 10) res2: Array[Int] = Array(20, 40, 60) ~~~ # 常用方法 **求和** ~~~ scala> arr res3: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7) scala> arr.sum res4: Int = 28 //reduce匯總 scala> arr.reduce(_+_) res5: Int = 28 ~~~ **給初始值求和** ~~~ scala> arr.fold(10)(_+_) res1: Int = 38 ~~~ **求最大值** ~~~ arr.max ~~~ **切分和壓平** flatten和map() ~~~ scala> val a = Array("a b c", "d e f", "h i j") a: Array[String] = Array(a b c, d e f, h i j) scala> a.map(_.split(" ")) res1: Array[Array[String]] = Array(Array(a, b, c), Array(d, e, f), Array(h, i, j)) scala> a.flatMap(_.split(" ")) res4: Array[String] = Array(a, b, c, d, e, f, h, i, j) ~~~ # 轉換為String ~~~ scala> val arr2 = Array(1,2,3) arr2: Array[Int] = Array(1, 2, 3) scala> arr2.mkString(",") res4: String = 1,2,3 ~~~ # 多維數組 ## 定義 ~~~ scala> val arr4 = Array.ofDim[Int](3, 4) arr4: Array[Array[Int]] = Array(Array(0, 0, 0, 0), Array(0, 0, 0, 0), Array(0, 0, 0, 0)) scala> arr4.mkString(" ") res16: String = [I@22b8eaf0 [I@50dfceff [I@26a5007 scala> for(x <- arr4) println(x.mkString(",")) 0,0,0,0 0,0,0,0 0,0,0,0 ~~~ 賦值 ~~~ scala> arr4(1)(2) = 1 ~~~ # 與java數組互相轉換 scala數組轉java數組 ~~~ import scala.collection.mutable.ArrayBuffer val arr4 = ArrayBuffer("1", "2", "3") // scala to java import scala.collection.JavaConversions.bufferAsJavaList val javaArr = new ProcessBuilder(arr4) println(javaArr.command()) ~~~ java數組轉scala數組 ~~~ import scala.collection.mutable.ArrayBuffer val arr4 = ArrayBuffer("1", "2", "3") //_表示導入這個包下的所有 import scala.collection.JavaConversions._ import scala.collection.mutable.Buffer // scala to java val javaArr = new ProcessBuilder(arr4) //java to scala val scalaArr: Buffer[String] = javaArr.command() println(scalaArr) ~~~