Thursday, August 28, 2014

Quicksort Sorting Algorithm in Java

Quicksort algorithm is one of the most used sorting algorithm, especially to sort large list and most of the programming languages, library have implemented it in one or another way. In Java, Arrays.sort() method sorts primitive data types using double pivot Quicksort algorithm, authored by Joshua Bloach and others. This implementation provides better performance for lot of data sets, where traditional quicksort algorithm reduced into quadratic performance. This method also uses MergeSort, another good sorting algorithm, to sort objects. QuickSort implementations are also available in C++ STL library. Have you ever thought why quicksort is so popular? because on average it is one of the fastest sorting algorithm we have. On average quicksort is a O(n log n) algorithm, while it's worst case is O(n^2), which is much better comparing with Bubble Sort or Insertion Sort. It's also one of the popular algorithm interview question, so as a programmer you must know how QuickSort works as well as how to implement Quicksort in Java or any other programming language. One of the most important thing interviewer look in your quicksort implementation is choice of pivot and whether you are sorting in place or not. In "in-place" sorting, actual sorting takes place in same array and no additional space is needed. Due to this reason, quicksort is very efficient in sorting large list of numbers, as no additional memory is required, a very space efficient sorting algorithm. Quicksort is also one of the naturally recursive algorithm and serves a good exercise for Java programmers to master art of recursion.

Tuesday, August 26, 2014

2 Examples to Convert Byte[] array to String in Java

Converting a byte array to String seems easy but what is difficult is, doing it correctly. Many programmers make mistake of ignoring character encoding whenever bytes are converted into a String or char or vice versa. As a programmer, we all know that computer's only understand binary data i.e. 0 and 1. All things we see and use e.g. images, text files, movies, or any other multi-media is stored in form of bytes, but what is more important is process of encoding or decoding bytes to character. Data conversion is an important topic on any programming interview, and because of trickiness of character encoding, this questions is one of the most popular String Interview question on Java Interviews. While reading a String from input source e.g. XML files, HTTP request, network port, or database, you must pay attention on which character encoding (e.g. UTF-8, UTF-16, and ISO 8859-1) they are encoded. If you will not use the same character encoding while converting bytes to String, you would end up with a corrupt String which may contain totally incorrect values. You might have seen ?, square brackets after converting byte[] to String, those are because of values your current character encoding is not supporting, and just showing some garbage values.

Tuesday, August 19, 2014

15 Java NIO, Socket, and Networking Interview Questions Answers

Networking and Socket Programming is one of the important area of Java programming language, especially for those programmers, who are working in client server based applications. Knowledge of important protocols e.g. TCP and UDP in detail is very important, especially if you are in business of writing high frequency trading application, which communicate via FIX Protocol or native exchange protocol. In this article, we will some of the frequently asked questions on networking and socket programming, mostly based around TCP IP protocol. This article is kinda light on NIO though, as it doesn't include questions from multiplexing, selectors, ByteBuffer and FileChannel but it does include classical questions like difference between IO and NIO. Main focus of this post is to make Java developer familiar with low level parts e.g. how TCP and UDP protocol works, socket options and writing multi-threaded servers in Java. Questions discussed here is not really tied up with Java programming language, and can be used in any programming language, which allows programmers to write client-server applications. By the way, If you are going for interview on Investment banks for core Java developer role, you better prepare well on Java NIO, Socket Programming, TCP, UDP and Networking along with other popular topics e.g. multi-threadingCollections API and Garbage Collection tuning. You can also contribute any question, which is asked to you or related to socket programming and networking and can be useful for Java interviews.

Thursday, August 14, 2014

Bubble Sort Algorithm in Java with Example

Bubble Sort is the first sorting algorithm I learned during my college day, and after so many years it's the one I remember by heart. It's kind of weird that one of the most popular sorting algorithm is also one of the worst performing sorting algorithm. Bubble sort's average case performance is in O(n^2), which means as the size array grows, the time it take to sort that array increases quadratic. Due to this reason, bubble sort is not used in production code, instead quick sort and merge sort are preferred over it. In fact, Java's own Arrays.sort() method, which is the easiest way to sort an array in Java also uses two pivot quicksort to sort primitive array and stable mergesort algorithm to sort object arrays.

Tuesday, August 12, 2014

How to find all Pairs in Array of Integers whose Sum is equal to a given Number

Practising coding problems are very important to do well in any programming interview. You should at your best on data-structures like an array, linked list, and string to clear any programming interview and believe me, you can not do this in one day or one week. It's rather a long process of learning through coding, and that's where these small coding problems help. Today, we are going to look at another interesting programming question from the array; write a program to find all pairs of integers whose sum is equal to a given number. For example if input integer array is {2, 6, 3, 9, 11} and given sum is 9, output should be {6,3}. Sounds simple? maybe, but this exact question has appeared in a technical interview at Amazon, Microsoft, Facebook and couple of another fortune five tech companies in past. Many of you might already heard about this question and some of you may already know the solution to this problem as well, but it's not enough to know just the answer. In a programming interview, many things matter apart from correct solution. For example, first thing Interviewer look is whether a candidate can ask right questions or not. So before jumping straight to coding, spare a second or two to think about the problem and clear any doubt you may have. For example, you can ask following questions based upon problem statement given above :

Friday, August 8, 2014

Difference between getPath(), getCanonicalPath() and getAbsolutePath() of File in Java

File API is very important one in Java, it gives access of File system to Java programs. Though Java's file API is rich, there are lot of subtleties to know when you use them. One of the common query programmer's has about file path is difference between getPath(), getCanonicalPath() and getAbsolutePath() methods, why there are three methods to get file path and what happens if you call getPath() in place of getCanonicalPath(). By the way, before understanding difference between getPath(), getAbsolutePath() and getCanonicalPath() let's understand the concept behind this methods, i.e. difference between path, absolute path, and canonical path.

Monday, August 4, 2014

How to Send Email from Java Program with Example

Sending Email from Java program is a common requirement. It doesn't matter whether you are working on core Java application, web application or enterprise Java EE application, you may need to send email to alert support personal with errors, or just send email to users on registration, password reset or asking them to confirm their email after registration. There are many such scenarios, where you need ability to send emails from Java program. In mature applications, you already have a module or library dealing with all king of email functionality and issues e.g. ability to send attachments, images, including signatures and other rich text formatting on emails, but if you have to code something from scratch then Java's Mail API is perfect place.

Friday, August 1, 2014

How to See difference between two Files in Eclipse - Text Comparision

One of the common task for every programmer is is to compare two files and find out difference between them. You would do this while comparing same file from different release version or from different environment to find out exactly what has changed. Though there are lot of good tools already exists to compare two files e.g. diff command in UNIX, Win Merge and Beyond compare in Windows, they are external tools. Beyond compare is not even free, but to be frank it's worth of money. I would like to compare two files directly from Eclipse to avoid switching to another program for a simple task. Actually, I have been using Beyond compare from long time, but I have practising to do every task ( which I can ) from Eclipse to save time by avoiding transition between multiple applications.