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LongStream reduce(long identity, LongBinaryOperator op) in Java with Examples

  • Last Updated : 06 Dec, 2018

LongStream reduce(long identity, LongBinaryOperator op) performs a reduction on the elements of this stream, using the provided identity value and an associative accumulation function, and returns the reduced value.

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 :

long reduce(long identity,  LongBinaryOperator op)

Parameters :



  • identity : The identity value for the accumulating function.
  • 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 : The result of the reduction.

Example 1 :




// Java code for LongStream reduce
// (long identity, LongBinaryOperator op)
import java.util.*;
import java.util.stream.LongStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating a LongStream
        LongStream stream = LongStream.of(1L, 3L, 5L, 7L, 9L);
  
        // Using LongStream reduce
        // (long identity, LongBinaryOperator op)
        long answer = stream.reduce(0, (num1, num2)
                                           -> (num1 + num2));
  
        // Displaying the result
        System.out.println(answer);
    }
}

Output :

25

Example 2 :




// Java code for LongStream reduce
// (long identity, LongBinaryOperator op)
import java.util.*;
import java.util.stream.LongStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating a LongStream
        LongStream stream = LongStream.range(3L, 7L);
  
        // Using LongStream reduce
        // (long identity, LongBinaryOperator op)
        long answer = stream.reduce(0, (num1, num2)
                                           -> (num1 * num2) - (num1 - num2));
  
        // Displaying the result
        System.out.println(answer);
    }
}

Output :

291

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