EnumSet and EnumMap

EnumSet

EnumSet is a Set implementation specifically designed for use with enum types. It is a highly optimized collection that is more efficient than HashSet when dealing with enums.

Features of EnumSet

• Specialized for Enums: It can only store enum values.

• Efficient: It uses bit vectors internally, making it much faster and more memory efficient than HashSet when working with enums.

• No Null Values: It does not allow null elements. Attempting to add null will throw a NullPointerException.

• Order: The order of the enum constants in the EnumSet is determined by their natural order (the order in which the constants are declared in the enum class). We can also use a specific ordering by providing a comparator.

import java.util.EnumSet;

public enum LogLevel {
    ERROR, WARNING, INFO, DEBUG;
}

public class EnumSetExample {
    public static void main(String[] args) {
        // Create an EnumSet containing some enum constants
        EnumSet<LogLevel> logLevels = EnumSet.of(LogLevel.ERROR, LogLevel.WARNING);
        
        // Print the EnumSet
        System.out.println("Log levels: " + logLevels);

        // Add more values
        logLevels.add(LogLevel.INFO);
        System.out.println("After adding INFO: " + logLevels);

        // Remove a value
        logLevels.remove(LogLevel.WARNING);
        System.out.println("After removing WARNING: " + logLevels);

        // Create an EnumSet with all values
        EnumSet<LogLevel> allLogLevels = EnumSet.allOf(LogLevel.class);
        System.out.println("All log levels: " + allLogLevels);
    }
}

Log levels: [ERROR, WARNING]
After adding INFO: [ERROR, WARNING, INFO]
After removing WARNING: [ERROR, INFO]
All log levels: [ERROR, WARNING, INFO, DEBUG]

Methods in EnumSet:

• EnumSet.of(E... elements): Creates an EnumSet with the specified enum constants.

• EnumSet.allOf(Class<E> elementType): Creates an EnumSet containing all constants of the specified enum class.

• EnumSet.noneOf(Class<E> elementType): Creates an empty EnumSet.

• EnumSet.copyOf(Collection<? extends E> c): Creates an EnumSet containing all of the elements in the specified collection that are also enum constants of the same type.

EnumMap

EnumMap is a Map implementation that uses enum constants as keys. It is optimized for use with enums as keys and provides superior performance over regular HashMap when the keys are enums.

Features of EnumMap:

• Specialized for Enums: The keys in an EnumMap must be enum constants.

• Efficient: It is faster and uses less memory than a HashMap when the keys are enums, because it internally stores the mappings in an array, making lookups and insertions much faster.

• Ordering: The map is ordered based on the natural order of the enum constants (the order in which the constants are defined).

• Null Keys Not Allowed: It does not allow null keys. However, null values are allowed.

import java.util.EnumMap;

public enum LogLevel {
    ERROR, WARNING, INFO, DEBUG;
}

public class EnumMapExample {
    public static void main(String[] args) {
        // Create an EnumMap where the key is LogLevel, and the value is a description
        EnumMap<LogLevel, String> logLevelDescriptions = new EnumMap<>(LogLevel.class);

        // Add entries to the EnumMap
        logLevelDescriptions.put(LogLevel.ERROR, "Critical error");
        logLevelDescriptions.put(LogLevel.WARNING, "Warning message");
        logLevelDescriptions.put(LogLevel.INFO, "Informational message");

        // Print the EnumMap
        System.out.println("Log level descriptions: " + logLevelDescriptions);

        // Retrieve a value
        System.out.println("INFO level description: " + logLevelDescriptions.get(LogLevel.INFO));
    }
}

Log level descriptions: {ERROR=Critical error, WARNING=Warning message, INFO=Informational message}
INFO level description: Informational message

Methods in EnumMap:

• EnumMap(Class<K> keyType): Creates an empty EnumMap with the specified enum type as the key.

• EnumMap.put(K key, V value): Adds a key-value pair to the map.

• EnumMap.get(Object key): Retrieves the value associated with the given key.

• EnumMap.remove(Object key): Removes the entry for the specified key.

Comparison of EnumSet vs EnumMap:

Feature	EnumSet	EnumMap
Type	A Set of enum values	A Map where keys are enum values
Null Handling	Does not allow null elements	Does not allow null keys, but allows null values
Usage	Used when you need a collection of enum values without duplicates	Used when you need to associate values with enum constants
Efficiency	More memory-efficient and faster than HashSet	More memory-efficient and faster than HashMap for enums as keys
Ordering	Follows the natural order of enum constants	Follows the natural order of enum constants