Choosing the Right Map to use in Java

It is a very important thing in choosing the right map to use in Java development. Developers must have a clear understanding of all map implementation in java. And also, the right decision to choose map may increase your application performance. So, in this article, we will discuss how to choose the Right Map to use in Java based on your requirement. Choosing the Right Map to use in Java

Earlier we have looked at the HashMap internal implementation, LinkedHasHMap internal implementation and TreeMap internal implementation. So, it is very important to understand the internal implementation of all maps such as HashMap, LinkedHashMap, TreeMap, and HashTable. Also, you must able to do a brief comparison between the maps to guide us on which one fits where.

LinkedList Algorithms Interview Questions

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Implementation of maps in Java

There are following the implementation of the map interface in Java.

HashMap in Java

The HashMap class extends AbstractMap and implements Map interface. HashMap is a key and value collection in java. The HashMap stores the data in key and value format. It provides the basic implementation of the Map interface of Java. We can put a value with using a key and also we can access this value using that key. It uses a hash table to store the map. This allows the execution time of the get() method and the put() method to remain the same.

LinkedHashMap in Java

This class extends HashMap and maintains a linked list of the entries in the map, in the order in which they were inserted. This allows insertion-order iteration over the map. That is, when iterating a LinkedHashMap, the elements will be returned in the order in which they were inserted. You can also create a LinkedHashMap that returns its elements in the order in which they were last accessed.

TreeMap in Java

A TreeMap contains values based on the key. It implements the NavigableMap interface and extends AbstractMap class. The TreeMap class implements the Map interface by using a tree. A TreeMap provides an efficient means of storing key/value pairs in sorted order and allows rapid retrieval. It cannot have a null key but can have multiple null values.

HashTable in Java

Hashtable stores key/value pairs in a hash table. When using a Hashtable, you specify an object that is used as a key and the value that you want to be linked to that key. The key is then hashed, and the resulting hash code is used as the index at which the value is stored within the table. It is synchronized.

We have seen all implementations of the Map in Java, so, let’s move to discuss the choosing the right Map to use in Java in the next section.

Choosing the Right Map to use in Java

If you want to store your data into a map in a general purpose then a HashMap is a good option to choose. The HashMap provides rapid storage and retrieval operations. It is chaotic in nature because it stores unorderly arrangement of entries. That is why the HashMap performs poorly in cases where there is a lot of iteration as the entire capacity of the underlying array affects traversal.

Collisions happen when 2 distinct keys generate the same hashCode() value. Multiple collisions are the result of bad hashCode() algorithm. The more the collisions the worse the performance of the hashMap.

In case, you want to store your data into a map in an order to the entries, a LinkedHashMap is a better choice. It is very similar to HashMap with the good attributes as maintain an order of insertion. It performs better where there is a lot of iteration because only the number of entries is taken into account regardless of capacity.

You can go with a HashTable where you want to put synchronization in Map.

A TreeMap can also be a good choice in case you want to store your data should be sorted. Remember, a TreeMap provides sorting based on the Key rather than value. At the negative side, a TreeMap offers worse general performance than the other alternatives such as HashMap and LinkedHashMap.