我们如何在Java 9中实现Stream API的方法？

Stream.iterate() ：此方法可以用作传统for循环的流版本替代。

Stream.takeWhile()：此方法可以在 while 循环中使用，在满足条件时取值。

Stream.dropWhile()：此方法可以在while 循环在满足条件时删除值。

在下面的示例中，我们可以实现静态方法：iterate()、takeWhile( )、 和 Stream API 的 dropWhile() 方法。

示例

import java.util.Arrays;
import java.util.Iterator;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamAPITest {
   public static void main(String args[]) {
      String[] sortedNames = {"Adithya", "Bharath", "Charan", "Dinesh", "Raja", "Ravi", "Zaheer"};

      System.out.println("[Traditional for loop] Indexes of names starting with R = ");
      for(int i = 0; i < sortedNames.length; i++) {
         if(sortedNames[i].<strong>startsWith</strong>("R")) {
            System.out.println(i);
         }
      }
      System.out.println("[Stream.iterate] Indexes of names starting with R = ");
      <strong>Stream.iterate</strong>(0, i -> i < sortedNames.length, i -> ++i).<strong>filter</strong>(i -> sortedNames[i].startsWith("R")).<strong>forEach</strong>(System.out::println);

      String namesAtoC = <strong>Arrays.stream</strong>(sortedNames).<strong>takeWhile</strong>(n -> n.<strong>charAt</strong>(0) <= 'C')
.<strong>collect</strong>(Collectors.joining(","));

      String namesDtoZ = <strong>Arrays.stream</strong>(sortedNames).<strong>dropWhile</strong>(n -> n.charAt(0) <= 'C')
.<strong>collect</strong>(Collectors.joining(","));

      System.out.println("Names A to C = " + namesAtoC);
      System.out.println("Names D to Z = " + namesDtoZ);
   }
}

输出

<strong>[Traditional for loop] Indexes of names starting with R =
4
5
[Stream.iterate] Indexes of names starting with R =
4
5
Names A to C = Adithya,Bharath,Charan
Names D to Z = Dinesh,Raja,Ravi,Zaheer</strong>

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