Solving ‘name’ in ‘enum’ is final and cannot be overridden (Kotlin)

Have you ever encountered the error message "‘name’ in ‘enum’ is final and cannot be overridden" while working with enums in Kotlin? This issue often arises when attempting to override the name property in an enum class, and it can be frustrating to deal with. However, fear not! In this article, we'll delve into what causes this error and explore effective solutions to overcome it. By the end, you'll have a clear understanding of how to work around this limitation in Kotlin.

Understanding the Error

When we attempt to override the name property in an enum class in Kotlin, we are met with the error message "‘name’ in ‘enum’ is final and cannot be overridden." This occurs because the name property in an enum class is treated as a final property, meaning that it can't be modified or overridden by default.

Example Scenario

Let's consider a scenario where we have an enum class representing different types of fruits:

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1enum class Fruit {
2    APPLE, BANANA, ORANGE;
3
4    var displayName: String = ""
5        get() {
6            return field
7        }
8        set(value) {
9            field = value
10        }
11
12    override fun toString(): String {
13        return if (displayName.isNotEmpty()) displayName else super.name
14    }
15}

In this example, we've defined a displayName property within the enum class Fruit to provide a custom name for each fruit type. Here, we attempt to override the toString() method to return the custom display name if it's set, falling back to the default enum name otherwise.

Solutions

1. Using when Expression

One way to address the inability to override the name property directly is to use a when expression to map the enum values to custom names. Let's modify our previous example to achieve this:

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1enum class Fruit {
2    APPLE, BANANA, ORANGE;
3
4    var displayName: String = ""
5        get() {
6            return field
7        }
8        set(value) {
9            field = value
10        }
11
12    fun getCustomName(): String {
13        return when (this) {
14            APPLE -> "Apple"
15            BANANA -> "Banana"
16            ORANGE -> "Orange"
17        }
18    }
19}

By utilizing a when expression within the getCustomName() function, we're able to return custom names based on the enum values without directly overriding the name property.

2. Storing Custom Names in Enum Constants

Another approach involves storing custom names as properties within the enum constants themselves. Let's modify our enum example once more to demonstrate this technique:

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1enum class Fruit(val displayName: String) {
2    APPLE("Apple"), BANANA("Banana"), ORANGE("Orange");
3
4    override fun toString(): String {
5        return displayName
6    }
7}

In this updated example, we've added a displayName property to each enum constant in the Fruit enum. By doing so, we can simply override the toString() method to return the custom name associated with each enum value.

In your future Kotlin projects, keep these solutions in mind to effortlessly manage and customize enum representations based on your specific requirements!