Java EnumMap put() Method

The EnumMap.put() method in Java is used to associate the specified value with the specified key 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.put() can be used effectively.

Table of Contents

1. Introduction
2. put Method Syntax
3. Examples
   • Basic Usage of put Method
   • Updating an Existing Entry
4. Real-World Use Case
   • Example: Managing Day-specific Tasks
5. Conclusion

Introduction

The EnumMap.put() method is a member of the EnumMap class in Java. It allows you to associate a specific value with a specific enum key. If the map previously contained a mapping for the key, the old value is replaced by the specified value.

put() Method Syntax

The syntax for the put method is as follows:

public V put(K key, V value)

• Parameters:
  • key: The key with which the specified value is to be associated.
  • value: The value to be associated with the specified key.
• Returns: The previous value associated with the key, or null if there was no mapping for the key.

Examples

Basic Usage of put Method

The put method can be used to add key-value pairs to an EnumMap.

Example

import java.util.EnumMap;

public class EnumMapPutExample {
    // 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 EnumMap
        System.out.println("Tasks for the week: " + tasks);
    }
}

Output:

Tasks for the week: {MONDAY=Go to gym, TUESDAY=Attend meeting, WEDNESDAY=Work from home}

Updating an Existing Entry

If the specified key is already present in the EnumMap, the put method will update the key with the new value.

Example

import java.util.EnumMap;

public class EnumMapUpdateExample {
    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");

        // Updating the entry for TUESDAY
        tasks.put(Day.TUESDAY, "Client call");

        // Printing the EnumMap
        System.out.println("Updated tasks for the week: " + tasks);
    }
}

Output:

Updated tasks for the week: {MONDAY=Go to gym, TUESDAY=Client call}

Real-World Use Case

Example: Managing Day-specific Tasks

A common real-world use case for EnumMap.put() is managing day-specific tasks for a week.

Example

import java.util.EnumMap;

public class TaskManager {
    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 tasks for the week
        for (Day day : Day.values()) {
            System.out.println(day + ": " + tasks.get(day));
        }
    }
}

Output:

MONDAY: Go to gym
TUESDAY: Attend meeting
WEDNESDAY: Work from home
THURSDAY: Team lunch
FRIDAY: Project presentation
SATURDAY: Family time
SUNDAY: Rest day

In this example, EnumMap.put() is used to manage tasks associated with each day of the week, making it easy to organize and retrieve day-specific tasks.

Conclusion

The EnumMap.put() method in Java provides a way to associate specific values with specific enum keys. By understanding how to use this method, you can efficiently manage collections of key-value pairs where the keys are enum constants. This method allows you to add and update entries in an EnumMap, making it a versatile tool for managing data in various scenarios.