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Wednesday, August 26, 2015

How to calculate Large Factorials using BigInteger in Java?

Factorial of numbers greater than or equal to 13 cannot be found using primitive int data type as shown in our earlier factorial solution due to overflow. These factorials are too large to fit in an int variable, whose maximum value is just 2147483647 (2^31 -1). Even if we use the long data type, factorials greater than or equal to 21 will generate an overflow. To find factorial of anything above 21, you need to use the BigInteger class from java.math package. As name suggests, BigInteger class is designed to hold really large integer value, something which is even bigger than maximum value of long primitive e.g. 2^63 -1 or 9223372036854775807L. You also need to change the way we calculate factorial for smaller number. You can not use recursion to calculate factorial of a larger number instead we need to use for loop for that.

Monday, August 24, 2015

Difference between HashMap, LinkedHashMap and TreeMap in Java

Map is one of the most important data structure from Java Collection Framework.  It provides hash table data structure functionality with it's rich implementations like HashMap, Hashtable, LinkedHashMap and little bit of sorting with TreeMap. So if you are looking to store key value pairs in Java program,  you have wide range of choices available depending upon your requirement. Main difference between LinkedHashMap, TreeMap and HashMap comes in there internal implementation and specific features, which makes them useful in certain scenarios. For example, HashMap is a general purpose Map (hash table data structure), which should be used whenever you need a hashing based data structure for storing your mappings (key value pairs). TreeMap provides you sorting, on top of hashing offered by Map interface, which means you can not only retrieve elements in constant time i.e. O(1) time, but also iterate through those mapping in a predefined sorted order, but you need to pay heavy price to keep mappings in sorted order. On the other hand, LinkedHashMap is a compromise between these two, it doesn't provide sorting but unlike HashMap, it provides ordering e.g. maintaining mappings in a order they are inserted into Map, known as insertion order or order on which they are accessed, called access order. Apart from these three popular Map implementation, you also have some special purpose Map implementations e.g. EnumMap for storing mapping with enum constants as keys,  it is highly optimized for enum constants. You also have a special map called WeakHashMap for creating a Garbage Collector friendly Cache, where values become eligible for garbage collection as soon as there is no other reference to them apart from keys in WeakHashMap.Then there is IdentityHashMap for creating a Map which uses identity instead of equality for comparing keys, since identity equality is rare, you get less number of collision on this Map and finally JDK 5 introduced ConcurrentHashMap for better scalability in multi-threaded environment, where number of reader threads clearly out numbers number of writer threads.

Thursday, August 20, 2015

5 Entertaining Posts from StackOverFlow - Must Read

StackOverFlow is great place to look for help, learn and participate, but it's also a great place to taste some real entertainment, contributed by programmers from all over the world. Though, due to strict policies of stackoverflow.com, most of entertaining post either are either gets closed or deleted, some of them remained to entertain programming community. Being a regular reader of StackOverFlow from long time, I have found couple of threads which are truly amazing, and has lot's of funny and entertaining content. Here I am going to share 5 of my favorite StackOverFlow posts, which I suggest you to read, if you get bored or you have some time to kill. By the way, don't forget to leave comments and let us know which is your favorite funny and entertaining threads in StackOverFlow.