Functional Programming - Reducing

In functional programming, reducing is a technique to reduce a stream of values to a single result by apply a function on all the values. Java provides reduce() function in a Stream class from Java 8 onwards. A stream has inbuilt reducing methods like sum(), average(), count() as well which works on all elements of the stream and returns the single result.

Example - Usage of Reducing

Following example shows how Reducing works.

FunctionTester.java

package com.tutorialspoint;

import java.util.stream.IntStream;

public class FunctionTester {
   public static void main(String[] args) {

      //1 * 2 * 3 * 4 = 24
      int product = IntStream.range(1, 5) 
         .reduce((num1, num2) -> num1 * num2)
         .orElse(-1); 

      //1 + 2 + 3 + 4 = 10
      int sum =  IntStream.range(1, 5).sum();

      System.out.println(product);
      System.out.println(sum);
   } 
}

Output

Run the FunctionTester and verify the output.

24
10