How to Efficiently Initialize a HashMap of HashMaps in Java

What are the best practices to avoid code repetition when initializing a HashMap of HashMaps in Java?

Map<String, Map<String, String>> mapOfMaps = new HashMap<>();

for (String outerKey : outerKeys) {
    mapOfMaps.put(outerKey, new HashMap<>());
}

Initializing a HashMap of HashMaps in Java can lead to code duplication if done in a traditional manner. This guide explains how to streamline the initialization process using best practices, ensuring your code remains clean and maintainable.

private Map<String, Map<String, String>> initializeMapOfMaps(Set<String> outerKeys) {
    Map<String, Map<String, String>> mapOfMaps = new HashMap<>();
    outerKeys.forEach(outerKey -> mapOfMaps.put(outerKey, new HashMap<>()));
    return mapOfMaps;
}

Causes

• Repetitive code when creating a new HashMap for each key.
• Lack of a dedicated method to handle the hashmap initialization.

Solutions

• Encapsulate the initialization logic in a method to avoid duplication.
• Consider using Java Streams for cleaner code.
• Utilize factory methods to create complex objects.

Mistake: Initializing each inner HashMap repeatedly in separate places

Solution: Encapsulate the logic in a single method that can be reused.

Mistake: Not using parameterized types leading to unchecked assignment warnings

Solution: Always specify the types in HashMap for better type safety.