HashMap vs. TreeMap in Java
HashMap and TreeMap both store values in the form of key-value pairs. There are built-in classes, in Java, for both of them.
Similarities
First, let’s take a brief look at the similarities between them:
- Manual synchronization is required for multi-threaded usage.
- Both use an Iterator for traversal.
- First incorporated in Java Development Kit 1.2.
Differences
The following are the differences between the two classes:
- Allows one null as a key and multiple nulls as values
- No iteration order
- Insertion/deletion requires O(1) time
- Implements the Map interface
- Nulls are only allowed as values
- Iterates in the natural order or the order provided by the Comparator
- Insertion/deletion requires O(log n) time, where n is the number of elements in the TreeMap
- Implements NavigableMap interface
Hierarchy
Class diagram showing a part of the hierarchy
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