HashMap, LinkedHashMap, and TreeMap in Java: What are the Key Differences?

Exploring the Distinctions between HashMap, LinkedHashMap, and TreeMap

In Java, these three data structures offer varying approaches to organizing and accessing data, each with its unique characteristics.

HashMap:

HashMap prioritizes efficiency, allowing for rapid retrieval and storage of data. It does not maintain any particular order and instead focuses on implementing a hash table to provide constant-time performance for most operations.

LinkedHashMap:

LinkedHashMap combines the benefits of HashMap and LinkedList, preserving the insertion order of elements. It employs a double-linked list structure, allowing for fast and ordered access to the data.

TreeMap:

TreeMap offers a sorted interface, maintaining the keys in ascending order. It relies on a Red-Black tree data structure, which allows for logarithmic time complexity for operations such as finding, inserting, and deleting elements.

Hashtables in Java:

Hashtables, no longer commonly used, preceded HashMap in Java and shared many similarities, namely their hash-based implementation. They were synchronized, ensuring thread safety, but at the cost of additional overhead.

Example:

Consider the following snippet, which illustrates the differences in output for the three structures:

Output:

HashMap (unordered):

TreeMap (sorted):

LinkedHashMap (insertion-ordered):

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