Map

Another member of the collections framework is the Map interface. This interface represents a collection of key-value pairs. Keys are unique, while values can be duplicated. That’s why we use the key to add and access the key-value pairs in a map. The commonly used implementations of the Map interface that we’ll discuss are HashMap and TreeMap.

HashMap

Probably the most popular one is HashMap. This is a widely used implementation of the Map interface that’s based on a hash table. Just like HashSet, it provides constant-time performance for basic operations. However, it does not guarantee any specific order of the keys. HashMap is suitable for situations where you need fast lookups and modifications, such as storing configuration settings or counting word occurrences in a piece of text. When the order is important, we can use TreeMap.

TreeMap

TreeMap is an implementation of the Map interface that’s based on a tree. It maintains key-value pairs...