LongStream reduce(LongBinaryOperator op) performs a reduction on the elements of this stream, using an associative accumulation function, and returns an OptionalLong describing the reduced value, if any.
A reduction operation or fold takes a sequence of input elements and combines them into a single summary result, such as finding the sum or maximum of a set of numbers. An operator or function op is associative if the following holds :
(a op b) op c == a op (b op c)
This is a terminal operation i.e, it may traverse the stream to produce a result or a side-effect. After the terminal operation is performed, the stream pipeline is considered consumed, and can no longer be used.
Syntax :
OptionalLong reduce(LongBinaryOperator op)
Parameters :
- OptionalLong : A container object which may or may not contain a long value. If a value is present, isPresent() will return true and getAsLong() will return the value.
- LongBinaryOperator : An operation upon two long-valued operands and producing a long-valued result.
- op : An associative, stateless function for combining two values.
Return Value : An OptionalLong describing the reduced value, if any.
Example 1 :
// Java code for LongStream reduce// (LongBinaryOperator op)import java.util.OptionalLong;import java.util.stream.LongStream; class GFG { // Driver code public static void main(String[] args) { // Creating a LongStream LongStream stream = LongStream.of(9L, 10L, 11L, 12L); // Using OptionalLong (a container object which // may or may not contain a non-null value) // Using LongStream reduce(LongBinaryOperator op) OptionalLong answer = stream.reduce(Long::sum); // if the stream is empty, an empty // OptionalLong is returned. if (answer.isPresent()) { System.out.println(answer.getAsLong()); } else { System.out.println("no value"); } }} |
Output :
42
Example 2 :
// Java code for LongStream reduce// (LongBinaryOperator op)import java.util.OptionalLong;import java.util.stream.LongStream; class GFG { // Driver code public static void main(String[] args) { // Creating a LongStream LongStream stream = LongStream.of(9L, 10L, 11L, 12L); // Using OptionalLong (a container object which // may or may not contain a non-null value) // Using LongStream reduce(LongBinaryOperator op) OptionalLong answer = stream.reduce((a, b) -> 2 * (a * b)); // if the stream is empty, an empty // OptionalLong is returned. if (answer.isPresent()) { System.out.println(answer.getAsLong()); } else { System.out.println("no value"); } }} |
Output :
95040