Java 9中Stream API添加了哪些新功能？

In Java 9, Oracle Corporation has added four useful new methods to Stream API. Those methods are iterate(), ofNullable(), takeWhile() and dropWhile().

import java.util.stream.Stream; public class StreamIterateMethodTest { public static void main(String[] args) { Stream.iterate(1, i -> i < 5, i -> i + 1).forEach(System.out::println); // iterate() } }

输出

1
2
3
4

ofNullable()

ofNullable()方法在元素不为null时返回一个stream对象。否则，返回一个空的stream。

示例

import java.util.stream.Stream;
public class StreamOfNullableMethodTest {
   public static void main(String[] args) {
      String str = "TutorialsPoint";
      Stream.ofNullable(str).forEach(System.out::println);    // ofNullable() method
   }
}

输出

TutorialsPoint

takeWhile()

The parameter passed to a takeWhile() method is a Predicate interface. This method takes an element of stream object from left to right until the condition of the Predicate object is no longer fulfilled.

Example

import java.util.stream.Stream;
public class StreamTakeWhileMethodTest {
   public static void main(String[] args) {
      Stream.of(1, 2, 3, 4, 5)
         .takeWhile(i -> i < 5)         // takeWhile() method
         .forEach(System.out::println);
   }
}

输出

1
2
3
4

dropWhile()

传递给 dropWhile() 方法的参数也是一个 Predicate 接口。它与 takeWhile() 方法相反。该方法从左到右依次传递流对象中的每个元素，并忽略满足条件的所有元素。一旦条件不再满足，它将返回所有剩余的元素。

示例

import java.util.stream.Stream;
public class StreamDropWhileMethodTest {
   public static void main(String[] args) {
      Stream.of(3, 2, 1, 4, 6, 7, 8, 9, 10)
            .dropWhile(i -> i < 5)     // dropWhile() method
            .forEach(System.out::println);
   }
}

输出

6
7
8
9
10

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