24-Map Explanation
The Map interface is part of the Java Collections Framework and does not extend the Collection interface. It is often used when you need to quickly look up values based on a specific key.
Key Characteristics of a Map:
Key-Value Pair: Each entry in a Map consists of a key and a value. Keys are unique, meaning that no two entries can have the same key, but values can be duplicated.
No Duplicates for Keys: A Map cannot contain duplicate keys. If you try to insert a key that already exists in the map, the existing value will be overwritten with the new value.
Null Keys and Values: Depending on the implementation, a Map may allow a single null key and multiple null values (e.g., HashMap), or it may not allow any null keys or values (e.g., TreeMap).
Efficient Lookup: Maps provide an efficient way to retrieve a value based on its key, typically in constant time (O(1) for HashMap).
HashMap:
Stores key-value pairs in a hash table.
Allows one null key and multiple null values.
Does not guarantee any specific order of the entries
LinkedHashMap:
Extends HashMap and maintains the order of entries based on their insertion order or access order (if configured).
Useful when you need to maintain the order of entries