java與scala數組及集合的基本操作對比

def main(args: Array[String]): Unit = {
 
    //new一個大小不變的數組
    val nums = new Array[Int](10) //會被初始化為0
 
    val s = Array("hello", "world") //使用兩個字符串初始化數組（記住，這裡不需要new）
 
    s(0) = "good bye" //使用()來訪問數組
 
}

public static void main(String[] args) {
    int[] nums = new int[10];
 
    String[] s = new String[]{"hello", "world"};
 
    s[0] = "goodbye";
}

def main(args: Array[String]): Unit = {
    val b = ArrayBuffer[Int]() //初始化
    //或者
    //    val b = new ArrayBuffer[Int]
 
    b += 1 //添加一個元素
    b += (1, 2, 3, 4, 5) //添加多個元素在末尾
 
    println(s"b:$b") //b:ArrayBuffer(1, 1, 2, 3, 4, 5)
 
    b ++= Array(8, 1, 34) //一次添加一個數組，註意這裡是數組
    println(s"b:$b") //b:ArrayBuffer(1, 1, 2, 3, 4, 5, 8, 1, 34)
 
    b.trimEnd(3) //移除最後三個元素
    println(s"b:$b") //b:ArrayBuffer(1, 1, 2, 3, 4, 5)
}

public static void main(String[] args) {
    List<Integer> list = new ArrayList<>();
    list.add(1);
 
    List<Integer> list2 = new ArrayList<>();
    list2.add(1);
    list2.add(2);
    list2.add(3);
    list2.add(4);
    list2.add(5);
    list.addAll(list2);
    //java一次要添加1，2，3，4，5就麻煩很多瞭
    // 當然使用guava的Lists.newArrayList看起來代碼會簡單些
    // 或者使用下面的Arrays.asList也會簡單些，最主要的原因是直接構造一個含有多個數字的list原生的java支持的不好
 
    System.out.println(list); //[1, 1, 2, 3, 4, 5]
 
    list.addAll(Arrays.asList(1, 2, 3, 4, 5));
    System.out.println(list); //[1, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5]
 
    //java沒有提供原生的，移除最後5個元素的函數
 
    list.add(1,6); //List一次隻能添加一個元素
    System.out.println(list); //[1, 6, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5]
 
    list.remove(1);
    System.out.println(list); //[1, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5]
 
    //list也不支持，移除第index上的連續n個數字
 
    Object[] array = list.toArray();//轉數組
    Arrays.asList(array); //轉list
}

def main(args: Array[String]): Unit = {
  val a = Array(1, 2, 3, 4, 5)
  for (i <- 0 until a.length) {
    println(s"i:$i value:${a(i)}")
  }
 
  println("-----------")
 
  //遍歷隔一個
  for (i <- 0 until a.length by 2) {
    println(s"i:$i value:${a(i)}")
  }
 
  println("-----------")
 
  //倒著遍歷
  for (i <- 0 until a.length reverse) {
    println(s"i:$i value:${a(i)}")
  }
 
  println("-----------")
 
  //如果不需要index
  for (ele <- a) {
    println(s"value:${ele}")
  }
}

public static void main(String[] args) {
    int[] a = new int[]{1, 2, 3, 4, 5};
 
    for (int i = 0; i < a.length; i++) {
        System.out.println("index:" + i + ",value:" + a[i]);
    }
 
    System.out.println("-----------------");
 
    //遍歷隔著2
    for (int i = 0; i < a.length; i += 2) {
        System.out.println("index:" + i + ",value:" + a[i]);
    }
 
    System.out.println("-----------------");
 
    //倒著遍歷
    for (int i = a.length - 1; i >= 0; i--) {
        System.out.println("index:" + i + ",value:" + a[i]);
    }
 
    System.out.println("-----------------");
 
    //不關心index
    for (int value : a) {
        System.out.println("value:" + value);
    }
}

int[] a = new int[]{1, 2, 5};

val a=Array(1,2,5)

final class Array[T](_length: Int) extends java.io.Serializable with java.lang.Cloneable {
  /** The length of the array */
  def length: Int = throw new Error()
  // The element at given index.
  def apply(i: Int): T = throw new Error()
  // Update the element at given index.
  def update(i: Int, x: T) { throw new Error() }
  //Clone the Array.
  override def clone(): Array[T] = throw new Error()
}

 /** Creates an array of `Int` objects */
  // Subject to a compiler optimization in Cleanup, see above.
  def apply(x: Int, xs: Int*): Array[Int] = {
    val array = new Array[Int](xs.length + 1)
    array(0) = x
    var i = 1
    for (x <- xs.iterator) { array(i) = x; i += 1 }
    array
  }