Java EnumMap Example

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EnumMap is a specialized Map implementation for use with enum type keys. It's part of the java.util package. Being both compact and efficient, the performance of EnumMap surpasses HashMap when the key is an enum type.

Key Points: 

Optimized for Enums: All keys in an EnumMap must come from a single enum type. 

Order: Keys are maintained in their natural order (the order in which the enum constants are declared). 

Nulls: While EnumMap does not allow null keys (because the key is an enum type), it does permit null values. 

Not Thread-Safe: EnumMap itself is not thread-safe. External synchronization is required if multiple threads modify an enum map concurrently and at least one of the threads modifies it.

Common Operations with EnumMap in Java

import java.util.EnumMap; // Define an enumeration for colors enum Color { RED, GREEN, BLUE } public class EnumMapDemo { public static void main(String[] args) { // 1. Initializing an empty EnumMap EnumMap<Color, String> colorMap = new EnumMap<>(Color.class); // 2. Putting values into EnumMap colorMap.put(Color.RED, "Apple"); colorMap.put(Color.GREEN, "Leaf"); colorMap.put(Color.BLUE, "Sky"); System.out.println("Color map: " + colorMap); // 3. Retrieving a value String blueItem = colorMap.get(Color.BLUE); System.out.println("Item associated with BLUE: " + blueItem); // 4. Checking if a specific key is present boolean hasRed = colorMap.containsKey(Color.RED); System.out.println("Map contains RED key: " + hasRed); // 5. Checking if a specific value is present boolean hasApple = colorMap.containsValue("Apple"); System.out.println("Map contains 'Apple' value: " + hasApple); // 6. Removing a key-value pair colorMap.remove(Color.GREEN); System.out.println("After removing GREEN key: " + colorMap); // 7. Getting the size of the map int size = colorMap.size(); System.out.println("Size of color map: " + size); } } 

Output:

Color map: {RED=Apple, GREEN=Leaf, BLUE=Sky} Item associated with BLUE: Sky Map contains RED key: true Map contains 'Apple' value: true After removing GREEN key: {RED=Apple, BLUE=Sky} Size of color map: 2 

Explanation:

1. Initializing an empty EnumMap that will have Color enum keys.

2. put: Adding key-value pairs to the map using the put method.

3. get: Retrieving the value associated with a specific key.

4. containsKey: Checking if a specific key is present in the map.

5. containsValue: Checking if a specific value is present in the map.

6. remove: Removing a specific key-value pair based on the key.

7. size: Getting the number of key-value pairs present in the map.

EnumMap is a specialized map implementation for use with enumeration type keys. It's compact and efficient, ensuring operations like get or put are faster than their HashMap counterparts when using enum keys.

Real-World Use Case: Tracking Employee Status with EnumMap

import java.util.EnumMap; // Define an enumeration for employee status enum Status { ONLINE, OFFLINE, ON_LEAVE, IN_MEETING } public class EmployeeStatusTracker { public static void main(String[] args) { // 1. Initializing an EnumMap to track employee status EnumMap<Status, String> employeeStatus = new EnumMap<>(Status.class); // 2. Assigning employees to their respective statuses employeeStatus.put(Status.ONLINE, "Ramesh"); employeeStatus.put(Status.OFFLINE, "Sunita"); employeeStatus.put(Status.ON_LEAVE, "Anil"); employeeStatus.put(Status.IN_MEETING, "Deepa"); // 3. Displaying the employees based on their status for (Status status : Status.values()) { System.out.println(status + ": " + employeeStatus.get(status)); } // 4. Changing the status of an employee employeeStatus.put(Status.ON_LEAVE, "Ramesh"); System.out.println("\nAfter updating status:"); for (Status status : Status.values()) { System.out.println(status + ": " + employeeStatus.get(status)); } } } 

Output:

ONLINE: Ramesh OFFLINE: Sunita ON_LEAVE: Anil IN_MEETING: Deepa After updating status: ONLINE: null OFFLINE: Sunita ON_LEAVE: Ramesh IN_MEETING: Deepa 

Explanation:

1. The Status enum represents different statuses an employee can have.

2. We create an EnumMap named employeeStatus that maps each status to an employee's name. EnumMap is efficient for enums as keys.

3. Initially, employees are assigned to their respective statuses and the map is displayed.

4. Later, Ramesh's status is updated from ONLINE to ON_LEAVE, and the updated map is displayed.

In this use case, EnumMap provides a clear and efficient way to represent and manage the statuses of employees. Enum keys ensure that there's a fixed set of possible statuses, making the system robust against invalid values.