Hashmap Vs Linkedhashmap Vs Treemap In Java?

1.	Hashmap Vs Linkedhashmap Vs Treemap In Java?
Answer» HashMap MAKES no guarantees as to the order of the map. LinkedHashMap maintains the insertion order of the elements which means if we iterate a LinkedHashMap we'll get the keys in the order in which they were inserted in the Map. TreeMap stores objects in sorted order. HashMap as well as LinkedHashMap allows one null as key, multiple values may be null though. TreeMap does not allow null as key. HashMap stores elements in a bucket which actually is an index of the array. LinkedHashMap also uses the same internal implementation, it also maintains a doubly-linked list running through all of its entries. TreeMap is a Red-Black tree based NavigableMap implementation. Performance WISE HashMap provides constant TIME performance O(1) for get() and put() method. LinkedHashMap also provides constant time performance O(1) for get() and put() method but in general a little slower than the HashMap as it has to maintain a doubly linked list. TreeMap provides guaranteed log(n) time cost for the containsKey, get, put and remove operations.

Answer»

HashMap MAKES no guarantees as to the order of the map.

LinkedHashMap maintains the insertion order of the elements which means if we iterate a LinkedHashMap we'll get the keys in the order in which they were inserted in the Map.

TreeMap stores objects in sorted order.
HashMap as well as LinkedHashMap allows one null as key, multiple values may be null though.

TreeMap does not allow null as key.
HashMap stores elements in a bucket which actually is an index of the array.

LinkedHashMap also uses the same internal implementation, it also maintains a doubly-linked list running through all of its entries.

TreeMap is a Red-Black tree based NavigableMap implementation.
Performance WISE HashMap provides constant TIME performance O(1) for get() and put() method.

LinkedHashMap also provides constant time performance O(1) for get() and put() method but in general a little slower than the HashMap as it has to maintain a doubly linked list.

TreeMap provides guaranteed log(n) time cost for the containsKey, get, put and remove operations.

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