Java EnumMap size() Method

The EnumMap.size() method in Java is used to determine the number of key-value mappings present in the map. This guide will cover the method's usage with examples, and we will also cover a real-world use case to show how EnumMap.size() can be used effectively.

Table of Contents

1. Introduction
2. size Method Syntax
3. Examples
   • Basic Usage of size Method
   • Working with Empty and Non-Empty Maps
4. Real-World Use Case
   • Example: Tracking Assigned Tasks
5. Conclusion

Introduction

The EnumMap.size() method is a member of the EnumMap class in Java. It returns the number of key-value mappings in the map, allowing you to determine how many entries are present in the EnumMap.

size() Method Syntax

The syntax for the size method is as follows:

public int size()

• Returns: The number of key-value mappings in this map.

Examples

Basic Usage of size Method

The size method can be used to find out how many entries are present in an EnumMap.

Example

import java.util.EnumMap;

public class EnumMapSizeExample {
    // Define an enum representing days of the week
    enum Day {
        MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
    }

    public static void main(String[] args) {
        // Create an EnumMap with Day as key and String as value
        EnumMap<Day, String> tasks = new EnumMap<>(Day.class);

        // Adding entries to the EnumMap
        tasks.put(Day.MONDAY, "Go to gym");
        tasks.put(Day.TUESDAY, "Attend meeting");
        tasks.put(Day.WEDNESDAY, "Work from home");

        // Printing the size of the EnumMap
        System.out.println("Number of tasks assigned: " + tasks.size());
    }
}

Output:

Number of tasks assigned: 3

Working with Empty and Non-Empty Maps

The size method returns 0 for an empty EnumMap and the correct count for a non-empty EnumMap.

Example

import java.util.EnumMap;

public class EnumMapEmptySizeExample {
    enum Day {
        MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
    }

    public static void main(String[] args) {
        // Create an empty EnumMap with Day as key and String as value
        EnumMap<Day, String> tasks = new EnumMap<>(Day.class);

        // Printing the size of the empty EnumMap
        System.out.println("Number of tasks assigned (initial): " + tasks.size());

        // Adding an entry to the EnumMap
        tasks.put(Day.MONDAY, "Go to gym");

        // Printing the size after adding an entry
        System.out.println("Number of tasks assigned (after adding): " + tasks.size());
    }
}

Output:

Number of tasks assigned (initial): 0
Number of tasks assigned (after adding): 1

Real-World Use Case

Example: Tracking Assigned Tasks

A common real-world use case for EnumMap.size() is tracking the number of tasks assigned for the week.

Example

import java.util.EnumMap;

public class TaskTracker {
    enum Day {
        MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
    }

    public static void main(String[] args) {
        // Create an EnumMap to manage tasks for each day
        EnumMap<Day, String> tasks = new EnumMap<>(Day.class);

        // Adding tasks for each day
        tasks.put(Day.MONDAY, "Go to gym");
        tasks.put(Day.TUESDAY, "Attend meeting");
        tasks.put(Day.WEDNESDAY, "Work from home");
        tasks.put(Day.THURSDAY, "Team lunch");
        tasks.put(Day.FRIDAY, "Project presentation");
        tasks.put(Day.SATURDAY, "Family time");
        tasks.put(Day.SUNDAY, "Rest day");

        // Printing the number of tasks assigned for the week
        System.out.println("Total number of tasks assigned for the week: " + tasks.size());
    }
}

Output:

Total number of tasks assigned for the week: 7

In this example, EnumMap.size() is used to count the total number of tasks assigned for the week, making it easy to track task assignments.

Conclusion

The EnumMap.size() method in Java provides a way to determine the number of key-value mappings in the map. By understanding how to use this method, you can efficiently manage and track the number of entries in collections where the keys are enum constants. This method allows you to get the size of an EnumMap, making it a versatile tool for managing data in various scenarios.