IntStream reduce(IntBinaryOperator op) in Java with Examples

IntStream reduce(IntBinaryOperator op) performs a reduction on the elements of this stream, using an associative accumulation function, and returns an OptionalInt 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 :

OptionalInt reduce(IntBinaryOperator op)

Parameters :

  • OptionalInt : A container object which may or may not contain a int value. If a value is present, isPresent() will return true and getAsInt() will return the value.
  • IntBinaryOperator : An operation upon two int-valued operands and producing an int-valued result.
  • op : An associative, stateless function for combining two values.

Return Value : An OptionalInt describing the reduced value, if any.

Example 1 :

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// Java code for IntStream reduce
// (IntBinaryOperator op)
import java.util.OptionalInt;
import java.util.stream.IntStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating an IntStream
        IntStream stream = IntStream.of(2, 3, 4, 5, 6);
  
        // Using OptionalInt (a container object which
        // may or may not contain a non-null value)
        // Using IntStream reduce(IntBinaryOperator op)
        OptionalInt answer = stream.reduce(Integer::sum);
  
        // if the stream is empty, an empty
        // OptionalInt is returned.
        if (answer.isPresent()) {
            System.out.println(answer.getAsInt());
        }
        else {
            System.out.println("no value");
        }
    }
}

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Output :

20

Example 2 :

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// Java code for IntStream reduce
// (IntBinaryOperator op)
import java.util.OptionalInt;
import java.util.stream.IntStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating an IntStream
        IntStream stream = IntStream.of(2, 3, 4, 5, 6);
  
        // Using OptionalInt (a container object which
        // may or may not contain a non-null value)
        // Using IntStream reduce(IntBinaryOperator op)
        OptionalInt answer = stream.reduce((a, b) -> (a * b));
  
        // if the stream is empty, an empty
        // OptionalInt is returned.
        if (answer.isPresent()) {
            System.out.println(answer.getAsInt());
        }
        else {
            System.out.println("no value");
        }
    }
}

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Output :

720


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