What are the new features added to Stream API in Java 9?

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

iterate()

The iterate() can be used as stream version replacement of traditional for-loops. This method has improved by adding another parameter, the Predicate interface that allows us to stop these endless numbers based on conditions defined with the Predicate interface.

Example

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()
   }
}

Output

1
2
3
4

ofNullable()

The ofNullable() method returns the stream object of an element if it is not null. Otherwise, it returns an empty stream.

Example

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
   }
}

Output

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);
   }
}

Output

1
2
3
4

dropWhile()

The parameter passed to a dropWhile() method is also a Predicate interface. It is opposite to the takeWhile() method. This method passes each element in a stream object from left to right and ignores all elements that satisfy the condition. Once the condition is no longer fulfilled, it takes all remaining elements to return.

Example

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);
   }
}

Output

6
7
8
9
10