Java HashMap size() Method

The HashMap.size() method in Java is used to get the number of key-value mappings in a HashMap. This guide will cover the method's usage, explain how it works, and provide examples to demonstrate its functionality.

Table of Contents

1. Introduction
2. size Method Syntax
3. Examples
   • Getting the Size of a HashMap
   • Real-World Use Case: Inventory Count
4. Conclusion

Introduction

The HashMap.size() method is a member of the HashMap class in Java. It allows you to determine the number of key-value mappings currently present in the HashMap. This can be useful when you need to know the number of entries in the map for various operations, such as iteration or validation.

size() Method Syntax

The syntax for the size method is as follows:

public int size()

• The method does not take any parameters.
• The method returns an integer value representing the number of key-value mappings in the HashMap.

Examples

Getting the Size of a HashMap

The size method can be used to get the number of key-value mappings in a HashMap.

Example

import java.util.HashMap;

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

        // Adding entries to the HashMap
        people.put("Ravi", 25);
        people.put("Priya", 30);
        people.put("Vijay", 35);

        // Getting the size of the HashMap
        int size = people.size();

        // Printing the size of the HashMap
        System.out.println("Size of HashMap: " + size);
    }
}

Output:

Size of HashMap: 3

Real-World Use Case: Inventory Count

In a real-world scenario, you might use the size method to get the count of items in an inventory system.

Example

import java.util.HashMap;

public class InventoryCount {
    public static void main(String[] args) {
        // Creating a HashMap with String keys (product names) and Integer values (quantities)
        HashMap<String, Integer> inventory = new HashMap<>();

        // Adding products to the inventory
        inventory.put("Laptops", 10);
        inventory.put("Smartphones", 15);
        inventory.put("Tablets", 5);

        // Getting the size of the inventory
        int inventorySize = inventory.size();

        // Printing the size of the inventory
        System.out.println("Number of products in inventory: " + inventorySize);
    }
}

Output:

Number of products in inventory: 3

Conclusion

The HashMap.size() method in Java provides a way to determine the number of key-value mappings in a HashMap. By understanding how to use this method, you can efficiently manage the contents of a HashMap and perform operations that depend on the number of entries. This method is useful in various scenarios, such as tracking the number of items in an inventory or validating the size of a data structure.