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EnumMap in Java

In the world of Java programming, data structures play a critical position in dealing with and organizing records correctly. One such facts structure that proves to be extremely beneficial is the EnumMap. EnumMaps are specialized Map implementations in Java designed to work with Enum keys. In this section, we will discuss EnumMap, exploring what they are, the way to use them efficaciously.

What is an EnumMap?

An EnumMap in Java is a high-overall performance implementation of the Map interface that makes use of Enum values as keys. It is a part of the java.util package and turned into introduced in Java 1.5. An EnumMap is mainly properly-suited for scenarios where the keys are constrained to a specific set of Enum values, as it affords a compact and efficient manner to save and get right of entry to records.

One of the primary advantages of the use of EnumMap is that they're relatively specialized, that allows for quicker and extra efficient operations compared to standard-reason Map implementations like HashMap. EnumMap may be notion of as an array of values where the index of each cost corresponds to the ordinal value of an Enum key. This direct mapping makes EnumMap rather green for a wide range of use cases.

Creating an EnumMap

To create an EnumMap, we need to specify the Enum elegance that defines the keys for the map. Let's keep in mind a simple example the use of an Enum to represent days of the week.



As we can see, the EnumMap continues the order of the Enum values and associates every value with a corresponding task.

Accessing Values in an EnumMap

Accessing values in an EnumMap is straightforward. We can use the get approach to retrieve the cost related to a selected Enum key. Here's an instance:


On WEDNESDAY, you should: Meetings

In this example, we retrieve the pastime associated with Day.WEDNESDAY and display it inside the output.

EnumMap vs. HashMap

Now that we have a basic expertise of EnumMaps, you would possibly wonder how they examine to the more normally used HashMap. EnumMaps have numerous uses while operating with Enum keys:

  • Efficiency: EnumMaps are particularly efficient because of their specialised nature. They are designed to work with a confined set of Enum keys and, as an end result, can outperform general-reason HashMaps in terms of memory utilization and get right of entry to velocity.
  • Type Safety: EnumMaps offer kind safety at collect time, because of this the compiler can catch any kind mismatches during development. It makes the code strong.
  • Enum Key Constraints: EnumMaps put in force that best keys of the required Enum type can be used, preventing accidental key type mismatches.
  • Compactness: EnumMaps are compact and use a simple array below the hood, making them reminiscence-efficient when running with a small set of Enum keys.
  • Iteration Order: EnumMaps maintain the natural order of Enum values, which can be useful when you want to iterate over the entries in a specific order.

While EnumMaps offer these advantages, it's critical to be aware that they're appropriate for unique use instances in which Enum keys are a natural suit. If your keys are not restricted to a restricted set of Enum values, a HashMap or another Map implementation is probably greater suitable.

Iterating Over an EnumMap

Iterating over an EnumMap is just like iterating over other Map implementations. You can use the improved for loop or other strategies like entrySet to traverse the entries.


On MONDAY, you should: Work
On TUESDAY, you should: Gym
On WEDNESDAY, you should: Meetings
On THURSDAY, you should: Study
On FRIDAY, you should: Relax
On SATURDAY, you should: Family Time
On SUNDAY, you should: Chores

In this example, we iterate over the EnumMap and print each entry that includes the Enum key (day of the week) and the associated activity.

EnumMap provide numerous strategies for appearing numerous operations, such as adding, getting rid of, and checking the existing of key-value pairs. Some of the normally used methods consist of:

put(Enum key, V value): Associates the required value with the desired Enum key in the EnumMap.

Get(Enum key): Returns the price associated with the desired Enum key, or null if the important thing isn't always gift.

remove(Enum key): Removes the key-cost pair related to the specified Enum key.

ContainsKey(Enum key): Checks if the EnumMap contains the specified key.

Size(): Returns the variety of key-value mappings inside the EnumMap.

Let's study an example that demonstrates these methods:


On WEDNESDAY, you should: Meetings
Removed SATURDAY from the EnumMap.
SUNDAY exists in the EnumMap: true
Number of entries in the EnumMap: 6

In this example, we carry out numerous operations on the EnumMap, including retrieving, disposing of, checking the existence of, and counting entries.

EnumMap Use Cases

EnumMaps are great perfect for scenarios wherein you have a finite and acknowledged set of Enum keys and also we need to accomplice specific values with every key. Here are some common use instances for EnumMaps.

  • Configuration: EnumMaps can be used to save configuration settings for distinct elements of an utility. For instance, we could use an Enum to represent different modules of your software, and an EnumMap to store configuration values for every module.
  • Days of the Week: As shown in previous examples, EnumMaps are perfect for representing and coping with activities or schedules for each day of the week.
  • State Machines: EnumMaps may be used to put in force state machines, wherein each state is an Enum and the transitions are described using the EnumMap.

Performance Considerations

EnumMaps are designed for efficiency when working with Enum keys. They are typically faster and more memory-efficient than general-purpose Map implementations like HashMap for a limited and known set of keys. However, it's essential to be aware of their strengths and limitations:

Iterating Order: EnumMaps hold the order of Enum values based on their ordinal positions. If we want a distinct ordering, we may want to do not forget an exclusive statistics shape.

Null Values: EnumMaps do no longer allow null keys, and attempts to apply null as a key will result in a NullPointerException.

In Summary, we have explored the sector of EnumMaps in Java, beginning from their basic principles and usage to extra advanced operations and use cases. EnumMaps are a specialized and efficient way to work with Enum keys and offer numerous uses in phrases of overall performance, type protection, and compactness.

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