Java HashMap values() Method

The HashMap.values() method in Java is used to return a Collection view of the values contained in the HashMap.

Table of Contents

1. Introduction
2. values Method Syntax
3. Examples
   • Iterating Over Values in a HashMap
   • Real-World Use Case: Calculating the Total Population
4. Conclusion

Introduction

The HashMap.values() method is a member of the HashMap class in Java. It provides a Collection view of the values contained in the HashMap. This can be useful for iterating over the values or performing bulk operations on the values without concern for the keys.

values() Method Syntax

The syntax for the values method is as follows:

public Collection<V> values()

• The method does not take any parameters.
• The method returns a Collection view of the values contained in the HashMap.

Examples

Iterating Over Values in a HashMap

The values method can be used to retrieve a Collection of the values in a HashMap, which can then be iterated over.

Example

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

public class ValuesExample {
    public static void main(String[] args) {
        // Creating a Map with String keys and Integer values
        Map<String, Integer> countries = new HashMap<>();

        // Adding entries to the HashMap
        countries.put("India", 91);
        countries.put("United States", 1);
        countries.put("Canada", 1);

        // Getting the collection of values
        Collection<Integer> values = countries.values();

        // Iterating over the values
        for (Integer value : values) {
            System.out.println("Value: " + value);
        }
    }
}

Output:

Value: 91
Value: 1
Value: 1

Real-World Use Case: Calculating the Total Population

In a real-world scenario, you might use the values method to retrieve all values from a HashMap and perform calculations such as finding the total population of countries stored in the map.

Example

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

public class TotalPopulation {
    public static void main(String[] args) {
        // Creating a Map with String keys (country names) and Integer values (population in millions)
        Map<String, Integer> countryPopulations = new HashMap<>();

        // Adding entries to the HashMap
        countryPopulations.put("India", 1391); // Population in millions
        countryPopulations.put("United States", 331); // Population in millions
        countryPopulations.put("Canada", 38); // Population in millions

        // Getting the collection of values (populations)
        Collection<Integer> populations = countryPopulations.values();

        // Calculating the total population
        int totalPopulation = populations.stream().mapToInt(Integer::intValue).sum();

        // Printing the total population
        System.out.println("Total Population (in millions): " + totalPopulation);
    }
}

Output:

Total Population (in millions): 1760

Conclusion

The HashMap.values() method in Java provides a way to retrieve a Collection view of the values contained in the HashMap. By understanding how to use this method, you can efficiently access and process the values in your map. This method is useful in various scenarios, such as iterating over values, performing calculations, and analyzing data stored in a HashMap. Using lambda expressions and streams with this method makes the code more concise and readable.