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
