Java - Stream API Improvements

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Streams were introduced in Java to help developers perform aggregate operations from a sequence of objects. With Java 9, few more methods are added to make streams better.

takeWhile(Predicate Interface) Method

Syntax

default Stream takeWhile(Predicate predicate)

takeWhile method takes all the values until the predicate returns false. It returns, in case of ordered stream, a stream consisting of the longest prefix of elements taken from this stream matching the given predicate.

Example

package com.tutorialspoint;

import java.util.stream.Stream;

public class Tester {
   public static void main(String[] args) {
      Stream.of("a","b","c","","e","f").takeWhile(s->!s.isEmpty())
         .forEach(System.out::print);		 
   } 
}

Output

takeWhile method takes all a, b, and c values, then once string is empty, it stopped executing.

abc

dropWhile(Predicate Interface)

Syntax

default Stream dropWhile(Predicate predicate)

dropWhile method throw away all the values at the start until the predicate returns true. It returns, in case of ordered stream, a stream consisting of the remaining elements of this stream after dropping the longest prefix of elements matching the given predicate.

Example

package com.tutorialspoint;

import java.util.stream.Stream;

public class Tester {
   public static void main(String[] args) {
      Stream.of("a","b","c","","e","f").dropWhile(s-> !s.isEmpty())
         .forEach(System.out::print);
      
      System.out.println();
      Stream.of("a","b","c","","e","","f").dropWhile(s-> !s.isEmpty())
         .forEach(System.out::print);
   } 
}

Output

dropWhile method drops a,b and c values, then once string is empty, it takes all the values.

ef
ef

iterate Method

Syntax

static  Stream iterate(T seed, Predicate hasNext, UnaryOperator next)

iterate method now has hasNext predicate as parameter which stops the loop once hasNext predicate returns false.

Example

package com.tutorialspoint;

import java.util.stream.IntStream;

public class Tester {
   public static void main(String[] args) {
      IntStream.iterate(3, x -> x < 10, x -> x+ 3).forEach(System.out::println);
   } 
}

Output

3
6
9

ofNullable

Syntax

static  Stream ofNullable(T t)

ofNullable method is introduced to prevent NullPointerExceptions and to avoid null checks for streams. This method returns a sequential Stream containing single element, if non-null, otherwise returns an empty Stream.

Example

package com.tutorialspoint;

import java.util.stream.Stream;

public class Tester {
   public static void main(String[] args) {
      long count = Stream.ofNullable(100).count();
      System.out.println(count);
  
      count = Stream.ofNullable(null).count();
      System.out.println(count);
   } 
}

Output

1
0