DoubleStream reduce(DoubleBinaryOperator op) performs a reduction on the elements of this stream, using an associative accumulation function, and returns an OptionalDouble 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 :
OptionalDouble reduce(DoubleBinaryOperator op)
Parameters :
- OptionalDouble : A container object which may or may not contain a long value. If a value is present, isPresent() will return true and getAsDouble() will return the value.
- DoubleBinaryOperator : An operation upon two double-valued operands and producing a double-valued result.
- op : An associative, stateless function for combining two values.
Return Value : An OptionalDouble describing the reduced value, if any.
Example 1 :
// Java code for DoubleStream reduce// (DoubleBinaryOperator op)import java.util.OptionalDouble;import java.util.stream.DoubleStream;  class GFG {      // Driver code    public static void main(String[] args)    {        // Creating a DoubleStream        DoubleStream stream = DoubleStream.of(1.2, 2.3, 3.4, 4.5);          // Using OptionalDouble (a container object which        // may or may not contain a non-null value)        // Using DoubleStream reduce(DoubleBinaryOperator op)        OptionalDouble answer = stream.reduce(Double::sum);          // if the stream is empty, an empty        // OptionalDouble is returned.        if (answer.isPresent()) {            System.out.println(answer.getAsDouble());        }        else {            System.out.println("Stream is empty");        }    }} |
Output :
11.4
Example 2 :
// Java code for DoubleStream reduce// (DoubleBinaryOperator op)import java.util.OptionalDouble;import java.util.stream.DoubleStream;  class GFG {      // Driver code    public static void main(String[] args)    {        // Creating a DoubleStream        DoubleStream stream = DoubleStream.of(1.2, 2.3, 3.4, 4.5);          // Using OptionalDouble (a container object which        // may or may not contain a non-null value)        // Using DoubleStream reduce(DoubleBinaryOperator op)        OptionalDouble answer = stream.reduce((a, b)                                  -> (a * b) * (a * b));          // if the stream is empty, an empty        // OptionalDouble is returned.        if (answer.isPresent()) {            System.out.println(answer.getAsDouble());        }        else {            System.out.println("Stream is empty");        }    }} |
Output :
9111992.471343633
