Java EnumMap

EnumMap is a specialized and efficient implementation of the Map interface in Java, designed to work specifically with enumerated types (enums). It is part of the Java Collections Framework and provides a way to represent and manipulate key-value pairs where the keys are enum constants and the values are associated data. Enum maps are highly efficient and provide some advantages over general-purpose maps when working with enums. Here are some key points about EnumMap:

1. Restricted to Enum Keys:

• EnumMap is designed to work only with enumerated types (enums). The keys in an EnumMap must be enum constants of a specific enum type.

1. Efficiency:

• EnumMap is highly efficient and optimized for memory usage and performance. It is implemented as an array, where the indices correspond to the ordinal values of the enum constants.

1. Type Safe:

• Because it’s restricted to enum keys, EnumMap is type-safe. You can’t accidentally use keys of the wrong type.

1. Creation:

• You can create an EnumMap by specifying the enum class for which the map is created. The enum class defines the set of valid keys.
• Example of creating an EnumMap:

   EnumMap<Day, String> dayActivities = new EnumMap<>(Day.class);

5. Methods:

• EnumMap provides methods for map operations like put(), get(), remove(), containsKey(), isEmpty(), and more.

5. Iteration Order:

• EnumMap maintains the natural iteration order of elements based on the order in which the enum constants are declared. This can be useful when iterating through the map.

5. No Null Keys:

• EnumMap does not allow null keys. If you attempt to use a null key, it will throw a NullPointerException.

5. Null Values:

• EnumMap allows null values.

Here’s an example of using EnumMap:

import java.util.EnumMap;

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

    public static void main(String[] args) {
        EnumMap<Day, String> dayActivities = new EnumMap<>(Day.class);

        // Adding key-value pairs
        dayActivities.put(Day.MONDAY, "Go to work");
        dayActivities.put(Day.FRIDAY, "Relax and have fun");

        // Retrieving values by key
        String mondayActivity = dayActivities.get(Day.MONDAY);
        System.out.println("Monday's activity: " + mondayActivity);

        // Iterating through key-value pairs
        for (Day day : Day.values()) {
            String activity = dayActivities.get(day);
            if (activity != null) {
                System.out.println(day + ": " + activity);
            }
        }
    }
}

In this example, we create an EnumMap to represent daily activities. The keys are enum constants from the Day enum, and the values are associated activities. EnumMap is a powerful and efficient way to work with enums and key-value pairs associated with enum constants.