Difference between EnumMap and HashMap in Java

Published May 12, 2022

Both EnumMaps and HashMaps are part of the Java.util package, and they implement the Map Interfaces and access its methods. Specifically, EnumMaps implements the map interface associated with enumeration types. HashMaps, on the other hand, are widely used in the implementation of hashtables.

Let's take a look at what makes Hashmaps and EnumMaps different in Java

The Differences between the EnumMaps and HashMaps

Here are the three most common differences between the EnumMaps and HashMaps

In general, the two types of implementation differ in their purposes. EnumMaps are designed for enumeration keys, whereas HashMaps are designed for hashtables.
The performance between the two differs. As a result of the specialised optimization done for Enum keys, they are more likely to perform better when used as the key object than the HashMap.
Finally, HashMap and EnumMap differ in the probability of collision. This is because the Enum is internally maintained as an array and is sorted by order with ordinal().

Example

import java.util.EnumMap;

import java.util.HashMap;

import java.util.Map;

public class EnumMaps_HashMaps {

public enum Planguages {

Python,

Java,

Kotlin,

Rubby;

}

public static void main(String[] args) {

EnumMap<Planguages, Integer> enumMap

= new EnumMap<>(Planguages.class);

enumMap.put(Planguages.Python, 1);

enumMap.put(Planguages.Java, 2);

enumMap.put(Planguages.Kotlin, 3);

enumMap.put(Planguages.Rubby, 4);

System.out.println("Our EnumMap: "

+ enumMap.size());

for (Map.Entry m : enumMap.entrySet()) {

System.out.println(m.getKey() + " "

+ m.getValue());

}

// HashMap

HashMap<Integer, String> mymap = new HashMap<>();

mymap.put(1, "Python");

mymap.put(2, "Java");

mymap.put(3, "Rubby");

System.out.println("Our map is: " + mymap.size());

for (Map.Entry a : mymap.entrySet()) {

System.out.println(a.getKey() + " "

+ a.getValue());

}

Output

Our EnumMap: 4

Python 1

Java 2

Kotlin 3

Rubby 4

Our map is: 3

1 Python

2 Java

3 Rubby

Keywords: EnumMaps, HashMaps

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