HashMap doesn't preserve any order by default. If order is required we need to sort it explicitly according to the requirement.
In this article I have tried to explain how to sort a HasMap based on values.
A Linked List is a dynamic data structure. The number of nodes in a list is not fixed and can grow and shrink on demand. Any application which has to deal with an unknown number of objects will need to use a linked list.
Linked lists and arrays are similar since they both store collections of data. The terminology is that arrays and linked lists store "elements" on behalf of "client" code. The specific type of element is not important since essentially the same structure works to store elements of any type. The size of the array is fixed where Linked List is a dynamic and also Inserting new elements at the front or in middle of an array is potentially expensive because existing elements need to be shifted over to make room.
MapReduce is a framework for processing large amount of data residing on hundreds of computers, its an extraordinarily powerful paradigm. MapReduce was first introduced by Google in 2004 MapReduce: Simplified Data Processing on Large Clusters.
In this article we'll see how MapReduce processes the data, I am considering the Word Count program as a example, yeah!! this is the worlds most famous MapReduce program!!