| The Java HashMap implementation of the MAP interface is BASED on hash tables. | Java TreeMap is a Map interface implementation based on a Tree structure. |
| The Map, Cloneable, and Serializable interfaces are implemented by HashMap. | NavigableMap, Cloneable, and Serializable interfaces are implemented by TreeMap. |
| Because HashMap does not order on keys, it allows for heterogeneous elements. | Because of the sorting, TreeMap allows homogenous values to be USED as a key. |
| HashMap is quicker than TreeMap because it offers O(1) constant-time performance for basic OPERATIONS such as to get() and put(). | TreeMap is slower than HashMap because it performs most operations with O(log(n)) performance, such as add(), remove(), and contains(). |
| A SINGLE null key and numerous null values are allowed in HashMap. | TreeMap does not allow null keys, however multiple null values are allowed. |
| To compare keys, it uses the Object class's equals() method. It is overridden by the Map class's equals() function. | It compares keys using the compareTo() method. |
| HashMap does not keep track of any sort of order. | The elements are arranged in chronological sequence (ascending). |
| When we don't need a sorted key-value pair, we should use the HashMap. | When we need a key-value pair in sorted (ascending) order, we should use the TreeMap. |
