Characteristic HashMap TreeMap LinkedHashMap Time complexity to search and insert O(1) O(log n) O(1) Iteration Order Random Sorted order according to the natural ordering Sorted order according to the insertion order Is Null key support Allowed Not allowed Allowed Is thread safe No, we need to collections utility to make thread safe No, we need to collections utility to make thread safe No, we need to collections utility to make thread safe Interface Map Map, SortedMap, NavigableMap Map Data structure support LinkedList DoublyLinkedList Application Normal processing, faster retrieval ConcurrentHashMap we can use as per the need Required when we do the sorting and navigable features need as per the use case. Required when we need to maintain the insertion order and when we need to implement the LRU cache. Key requirement equals() and hashcode() method need to overwritten Along with equals() and hashcode(), the comparator to implement. equals() and hashcode() method need to overwritten Syntax public class HashMap extends AbstractMap implements Map, Cloneable, Serializable public class TreeMap extends AbstractMap implements NavigableMap, Cloneable, Serializable public class LinkedHashMap extends HashMap implements Map