This content originally appeared on DEV Community and was authored by Felipe Jansen
Have you ever wondered how to efficiently store key-value pairs in Java? 
If so, let’s talk about two essential structures: Map and HashMap.
What is a Map?
Map is an interface in Java that represents a collection of key-value pairs, where each key is unique. This means you can use Map to map a specific key to a specific value, allowing for quick and efficient lookups.
Introducing HashMap
HashMap is a concrete implementation of the Map interface, based on the hash table data structure. It offers:
- O(1) complexity for insertion and lookup operations in most cases.
- Flexibility: allows null as a key and value.
- Performance: ideal for scenarios where the order of keys is not relevant.
Benefits of HashMap:
- Efficiency: Fast insertion, removal, and lookup operations.
- Simplicity: Easy to use and implement.
- Versatility: Can store any type of data.
Points to Consider:
- Unordered: The order of elements is not guaranteed.
- Synchronization: Not thread-safe by default. Use Collections.synchronizedMap for synchronization.
Understanding these structures can take your Java knowledge to the next level, providing more efficient and elegant solutions! 
Share your experiences with Map and HashMap in the comments! 
This content originally appeared on DEV Community and was authored by Felipe Jansen