10 Java Enum Best Practices

Enums are a powerful feature of the Java programming language. They provide a way to define a set of named constants, and can be used in a type-safe way.

However, there are a few best practices to keep in mind when using enums in your Java code. In this article, we’ll discuss 10 of those best practices. By following these best practices, you can make your code more readable, maintainable, and error-prone.

1. Enums should be immutable

If an enum is mutable, it means that its state can change after it’s been created. This can lead to all sorts of problems, such as:

– The enum could be in an inconsistent state (for example, if two threads are modifying the enum at the same time).
– The enum could be modified in a way that violates its invariants (for example, if an invalid state is introduced).
– The enum could be modified in a way that breaks compatibility with existing code (for example, if the order of the values in the enum is changed).

Making an enum immutable helps to avoid all of these problems.

2. Don’t use ordinal() to index arrays or collections

The ordinal() method returns the position of an enum constant in its enum declaration. For example, for the following enum:

public enum Status {
PENDING,
ACTIVE,
INACTIVE,
DELETED;
}
The ordinal values would be 0, 1, 2, and 3 respectively.

Now, let’s say you have an array of strings that need to be mapped to the enum constants. You might be tempted to do something like this:

String[] strings = {“pending”, “active”, “inactive”, “deleted”};

for (int i = 0; i < strings.length; i++) {
if (strings[i].equalsIgnoreCase(Status.values()[i].name())) {
System.out.println(“Match found: ” + Status.values()[i]);
}
}
However, this is a bad idea because it’s relying on the ordinal values of the enum constants, which can change if the enum is modified (for example, if a new constant is added).

A better way to do this would be to use a Map:

Map map = new HashMap<>();
map.put(“pending”, Status.PENDING);
map.put(“active”, Status.ACTIVE);
map.put(“inactive”, Status.INACTIVE);
map.put(“deleted”, Status.DELETED);

for (String s : strings) {
if (map.containsKey(s)) {
System.out.println(“Match found: ” + map.get(s));
}
}
This approach is more robust because it doesn’t rely on the ordinal values of the enum constants.

3. Use valueOf() instead of parsing yourself

When you use valueOf(), the enum is responsible for its own parsing. This means that if the enum values ever change, your code will still work because it’s using the enum’s built-in parsing logic.

On the other hand, if you parse the enum yourself, then you’re responsible for keeping your parsing logic up-to-date with the enum values. This can be error-prone and time-consuming.

So, to save yourself some headaches, use valueOf() instead of parsing enums yourself.

4. Avoid switch statements on enums

When you use a switch statement on an enum, the compiler generates a lookup table for the enum values. This can lead to performance issues because the lookup table is generated every time the switch statement is executed.

Additionally, if you add or remove enum values, the lookup table will need to be regenerated, which can cause compile-time errors.

It’s better to use if/else statements when working with enums. This avoids the need for a lookup table and ensures that your code will still compile even if you add or remove enum values.

5. Prefer instance fields over static fields

When you use static fields, all instances of the enum will share the same field. This can lead to unexpected results if the field is mutable. For example, let’s say you have an enum with a static field that keeps track of the number of times each enum value has been accessed.

If two threads are accessing the enum at the same time, they could both increment the field for the same enum value. As a result, the field would not accurately reflect the number of times that enum value had been accessed.

On the other hand, if you use instance fields, each enum value will have its own separate field. This means that there is no risk of one thread overwriting the field value for another thread.

6. Prefer getters over public fields

When you use public fields, your code becomes tightly coupled to the enum. This means that if you ever need to change the name of the field, you’ll also need to update all the places in your code where that field is used.

Getters, on the other hand, provide a layer of abstraction. This means that you can change the name of the field without having to update your code. Getters also have the advantage of being able to perform additional logic, such as validation.

7. Enum types with a small number of constant values are good candidates for singletons

When you have an enum type with only a few constant values, it’s likely that those constants will be used in many different places throughout your codebase. If each time you need to use one of those constants you have to create a new instance of the enum, that can lead to a lot of unnecessary object creation.

Creating a singleton enum is a way to avoid that problem. By creating a singleton, you can ensure that there is only one instance of the enum created, no matter how many times it’s used. This can help improve performance and save memory.

8. Consider using an enum map

Enum maps are specialized map implementations designed to work with enum keys. They offer better type safety and performance than using a regular map with an enum key.

If you’re working with an enum that has a lot of values, an enum map can help you manage them more effectively. It’s also a good idea to use an enum map if you need to associate data with each enum value.

9. If you need serialization, consider implementing it yourself

The default serialization provided by the JVM is not very robust. It can change between JVM implementations, and it doesn’t provide a lot of control over the format of the serialized data. If you need to serialize your enums, it’s best to implement your own serialization.

Not only will this give you more control over the format of the data, but it will also make your code more portable. If you ever need to move to a different JVM implementation, your serialization code will still work.

10. Make sure your equals and hashCode methods work properly

If you’re using an enum as the key in a Map, or as the value in a Set, then it’s important that your equals and hashCode methods are implemented correctly. The reason for this is that when the Map or Set calls your equals method, it will use the == operator to compare the object references, not the actual objects themselves.

This can lead to unexpected results, especially if you’re using a mutable enum. For example, let’s say you have an enum with two values: FOO and BAR. You add a FOO instance to a Set, and then later you add a BAR instance with the same value as the FOO instance. Even though the two instances have the same value, they’re not equal according to the == operator, so they’ll both be added to the Set.

To avoid this problem, you need to make sure your equals and hashCode methods take into account the actual values of the enum constants, not just the reference.