DoubleStream reduce(DoubleBinaryOperator op) in Java

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 :

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// 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");
        }
    }
}

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Output :

11.4

Example 2 :

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// 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");
        }
    }
}

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Output :

9111992.471343633


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In love with a semicolon because sometimes i miss it so badly)

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