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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<T> takeWhile(Predicate<? super T> 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<T> dropWhile(Predicate<? super T> 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 <T> Stream<T> iterate(T seed, Predicate<? super T> hasNext, UnaryOperator<T> 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 <T> Stream<T> 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
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