Mapping enum keys with EnumMaps

Sebastian DaschnerJanuary 22nd, 2018Last Updated: January 22nd, 2018

0 39 1 minute read

Here’s a type that has been around in the JDK for a while and that comes in handy when we want to define maps with enum types as keys: An EnumMap is a such as specialized Map.

We’ll create a map for a given enum:

public enum CoffeeType {
    ESPRESSO, POUR_OVER, FRENCH_PRESS
}

The EnumMap needs to be aware of the enum class at creation time:

Map<CoffeeType, String> favoriteCoffeeOrigins = new EnumMap<>(CoffeeType.class);

favoriteCoffeeOrigins.put(CoffeeType.ESPRESSO, "Ethiopia");
favoriteCoffeeOrigins.put(CoffeeType.POUR_OVER, "Colombia");
favoriteCoffeeOrigins.put(CoffeeType.FRENCH_PRESS, "Indonesia");

assertThat(favoriteCoffeeOrigins.get(CoffeeType.ESPRESSO)).isEqualTo("Ethiopia");

An EnumMap is much more efficient compared to a HashMap implementation. All basic map operations of this Java implementation are executed in constant time.

This post was reposted from my newsletter issue 017.

Published on Java Code Geeks with permission by Sebastian Daschner, partner at our JCG program. See the original article here: Mapping enum keys with EnumMaps

Opinions expressed by Java Code Geeks contributors are their own.