Calculate sum of all Map values in Java

This post will discuss how to calculate the sum of all values in a Map<?, Integer> in Java.

We can easily get a collection view of the values contained in this map using the values() method. Now the task is reduced to summing up all values in a collection. This can be done in several ways in Java:

1. Using Java 8

In Java 8 or above, the sum operation can be done trivially using Streams without any loops.

import java.util.HashMap;

import java.util.Map;

public class Main

{

public static void main(String[] args)

{

Map<String, Integer> persons = new HashMap<>();

persons.put("John", 25);

persons.put("Neil", 15);

persons.put("Rosy", 18);

int sum = persons.values().stream().mapToInt(Integer::intValue).sum();

System.out.println(sum); // 58

}

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We can also perform a reduction operation on stream elements using the reduce() method.

import java.util.HashMap;

import java.util.Map;

public class Main

{

public static void main(String[] args)

{

Map<String, Integer> persons = new HashMap<>();

persons.put("John", 25);

persons.put("Neil", 15);

persons.put("Rosy", 18);

int sum = persons.values().stream().reduce(0, Integer::sum);

System.out.println(sum); // 58

}

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2. Using for loop

Before Java 8, we can use replace the Stream API chain with a simple for loop:

import java.util.HashMap;

import java.util.Map;

public class Main

{

public static void main(String[] args)

{

Map<String, Integer> persons = new HashMap<>();

persons.put("John", 25);

persons.put("Neil", 15);

persons.put("Rosy", 18);

int sum = 0;

for (int value: persons.values()) {

sum += value;

}

System.out.println(sum); // 58

}

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That’s all about calculating the sum of all values in a Map<?, Integer> in Java.

Calculate sum of all Map values in Java

1. Using Java 8

2. Using for loop

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