Blog

Hey guys in this post we will discuss about reduce() of Stream API which is introduced in Java 8.

Introduction

• Many times we need to perform operations where a stream reduces to single resultant value, for example, maximum, minimum, sum, minus, product, divide etc. Reducing is the repeated process of combining all elements
• sum(), min(), max(), count(), etc are some examples of reduce operations. reduce() explicitly asks you to specify how to reduce the data that made it through the stream.
• Stream.reduce() is terminal method

Different variant of reduce() method

• reduce(BinaryOperator accumulator)
• reduce(T indentity, BinaryOperator accumulator)
• reduce(U indentity, BiFunction accumulator, BinaryOperator combiner)

reduce(BinaryOperator accumulator)

• It performs a reduction on the elements of the given stream, using given accumulation function
• accumulator – accumulator is a function for combining two values

#1 reduce() method with accumulator

import java.util.Arrays;
import java.util.stream.Stream;

public class Example2 {
	
	public static void main(String[] args) {
		
		int numbers[] = {1,2,3,4,5}; 
		String[] list = {"HP", "Lenovo", "Dell", "Macbook", "Acer"};
		
		Arrays.stream(numbers)
				.reduce((a, b)->a+b).ifPresent(System.out::println);
		
		Stream.of(10,20,30,40)
			.reduce(Integer::max)
			.ifPresent(System.out::println);
		
		Arrays.stream(list)
			.reduce((a, b) -> a+ " | "+b)
			.ifPresent(System.out::println);

	}
}	
//15
//40
// HP | Lenovo | Dell | Macbook | Acer

reduce(T indentity, BinaryOperator accumulator)

• indentity – the indentity value for the accumulating function
• accumulator – accumulator is a function for combining two values

#2 Reduce() with identity and accumulator

import java.util.Arrays;
import java.util.stream.Stream;

public class Example2 {
	
	public static void main(String[] args) {
		
		Integer numbers[] = {1,2,3,4,5}; 
		String[] list = {"HP", "Lenovo", "Dell", "Macbook", "Acer"};
		
		Integer resultOne = Stream.of(numbers)
					.reduce(100,  (x, y)-> x+y);
		System.out.println(resultOne);
		
		Integer resultTwo = Arrays.stream(numbers)
					.reduce(100, Integer::max);
		System.out.println(resultTwo);
		
		String resultThree = Stream.of(list)
					.reduce("Programming languages:",  (x, y)->x+" | "+y);
		System.out.println(resultThree);

	}
}	

Reduce(U indentity, BiFunction accumulator, BinaryOperator combiner)

• identity – the identity value for the combiner function
• accumulator – accumulator is function for incorporating additional element into result
• combiner – combiner is function for combining two values. combiner works with only parallelStream