HashSet and TreeSet both implement same interface i.e java.util.Set interface and they possess the quality of Set interface means duplicate elements are not allowed. Both HashSet and TreeSet are used to store unique elements, but HashSet doesn't care about any order and TreeSet keeps a thing in order. Ordering or sorting on TreeSet can be customized by using the Comparator interface, by default TreeSet uses elements of natural order for sorting, which is defined by the compareTo() method of java.lang.Comparable interface. What is the difference between HashSet and TreeSet is also one of the frequently asked Java interview questions, So you should know about similarities and differences between them?
What is fail safe and fail fast Iterator in Java?
Java Collections supports two types of Iterator, fail-safe and fail fast. The main distinction between a fail-fast and fail-safe Iterator is whether or not the underlying collection can be modified while it begins iterated. If you have used Collection like ArrayList then you know that when you iterate over them, no other thread should modify the collection. If the Iterator detects any structural change after iteration has begun e.g adding or removing a new element then it throws ConcurrentModificationException, this is known as fail-fast behavior and these iterators are called fail-fast iterator because they fail as soon as they detect any modification.
How to calculate Sum of Digits using Recursion in Java [Example]
This is the second part of our article to solve this coding interview question, how to find the sum of digits of an integer number in Java. In the first part, we have solved this problem without using recursion i.e. by using a while loop and in this part, we will solve it by using recursion. It's good to know different approaches to solving the same problem, this will help you to do well on coding interviews. While finding a recursive algorithm, always search for a base case, which requires special handling. Once you find the base case, you can easily code the method by delegating the rest of the processing to the method itself, i.e. by using recursion.
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