Javarevisited

How to Add Two Integer Numbers without using Plus + or ++ Arithmetic Operator in Java - Recursion example

2013-06-18T07:18:00.000-07:00

In this article, we will take a look on another interview question about adding two numbers, but without using + or ++ operator. Interview starts with a simple statement, Can you write a function to add two numbers (integers) without using + or plus arithmetic operator in Java? If you are good in maths, it wouldn’t take more than a second to say that, we can use subtraction or - operator to add two numbers because a-(-b)== a+b. Well that’s correct, but real question starts when interviewer quickly points out that, you can not use any arithmetic operator including +,-,*,/++ or --. Programming and Coding questions are integral part of any Java interview. You should always expect couple of questions like this, e.g. swapping two numbers without using temp variable. If you have been giving interviews, then you know that, it will eventually comes downs to bitwise operator in Java. Yes, we can add two numbers by using bitwise and bitshift operators, which is not arithmetic. Interviewer, will be happy by hearing bitwise operator, but he would like to see the code. Well, if you know binary arithmetic or how to add numbers in binary format, you may be familiar with fact than sum of two numbers can be obtained by using XOR operation and carry, by using AND operation. This is the fact, you must remember to solve this question or add two integers without using any arithmetic operator e.g. plus, minus etc. Sometime interviewer, may ask you to write both iterative and recursive solution of same question, Since recursion is another confusing programming technique, it's favored more during interviews. In this Java tutorial, we will see both recursive and iterative version of our add method, which calculate sum of two numbers without using arithmetic operator, but using bitshift and bitwise operators in Java.

Spring HelloWorld Example in Java using Dependency Injection

2013-06-13T06:47:00.000-07:00

In this Spring framework tutorial, we will learn how to write hello world example. This should be the first tutorial to start learning Spring framework, as it gets ball rolling and while coding and running this example, you learn a lot about Spring framework, Spring XSD files, required JAR file and more importantly how spring works.This Helloworld program in Spring framework is an example of classical Java hello world program, written using dependency Injection design pattern by using Spring Framework's IOC container. Spring is so far one of the most popular Java application framework, which promotes some best practices while writing Java application e.g. dependency Injection. Spring provides an IOC container to manage life-cycle of Spring beans and provides support to get beans any time from IOC container. Apart from Spring's IOC container, it also provide rich API to simply many of Java task e.g. JdbcTemplate help you to write JDBC code without taking care of boiler plate things like closing connection, statement, result-set etc. Similarly Spring framework also provides JmsTemplate to simply JMS related task e.g. sending and receiving messages in Java. I first learned about usefulness of Spring framework, while reading Expert Spring MVC and Web Flow, it first few chapters, which explains about how dependency injection provides improved testing, loose coupling and help in clean code. Those two chapters are so far my best read on Spring, and I also suggest to take a look. By the way in this Spring tutorial, we will see one of the most simple example of Dependency Injection e.g. Hello Example. Message to Hello class is provided by Spring framework using Dependency Injection.

How to Generate MD5 checksum for Files in Java

2013-06-11T06:02:00.000-07:00

MD5 checksums are good to verify integrity of files and It's easy to generate MD5 checksum in Java. Java provides couple of ways to generate MD5 checksum for any file, you can either use java.security.MessageDigest or any open source library like Apache commons codec or Spring. All 3 ways we have seen in our earlier article about generating MD5 hash for String is also applicable to generate MD5 checksum for any file. Since most of md5() or md5Hex() method takes byte[], you can simply read bytes from InputStream or pass to these md5 methods. Apache commons codec from version 1.4 also provides an overloaded method to accept InputStream, which makes generating checksum very easy in Java. For those who are not familiar with checksum, it's a fixed size datum generated from a block of data to detect any accidental change in data. Which means once you create checksum for a file, which is based on contents of file, any change on file e.g. adding white space, deleting a character will result in different checksum. By comparing stored checksum with current checksum, you can detect any change on File. It's good practice to provide checksum of WAR or JAR files to support teams for production release. In this Java tutorial we will learn how to create MD5 checksum for any file in Java.

How to get current URL, parameters and Hash tag using JQuery and JavaScript

2013-06-06T06:47:00.002-07:00

While dealing with current URL, many time you want to know what is the current URL path, What are the parameters, and what is the hash tag on URL. Hash tag is pretty important, if you are implementing tab structure using HTML and JQuery. To avoid confusion, let's take an example of URL: http://javarevisited.blogspot.com/2013/01/top-5-java-programming-books-best-good.html#ixzz2PGmDFlPd , in this example ixzz2PGmDFlPd is hash tag. Now, both JavaScript and JQuery provides convenient way to retrieve current URL in form of window.location object. You can use various properties of window.location JavaScript object e.g. window.location.href to get complete URL, window.location.pathname to get current path, and window.location.hash to get hash tag from current URL. If you like to use JQuery then you can get window.location as JQuery object and retrieve relevant properties using attr() function. If you are absolutely new in JQuery, and unaware of power of one of the most popular JavaScript framework, Head First JQuery is a good starting point. Being a fan of head first book, I always approach a new technology by an Head first title, it helped to learn a lot in short time, without spending time in trivial examples. By the way, In this web tutorial, we are going to retrieve current URL and hash tag using JavaScript and JQuery.

Why Favor Composition over Inheritance in Java and Object Oriented Programming

2013-06-04T08:24:00.002-07:00

Favor composition over inheritance is a one of the popular object oriented design principle, which helps to create flexible and maintainable code in Java and other object oriented languages. Many times I have seen people suggesting use composition instead of inheritance, in fact my favorite books like Head first Design Patterns, also advocates this design principle. Head first books, has its own way of explaining, why composition is better than inheritance and though its long its quite interesting and informative. It was the first chapter of this book, which helped me a lot on understanding this key OOPS concept. In this Java and OOPS tutorial, I have tried to summarize my experience around composition and inheritance in two main category, first, difference between composition and inheritance and second, when to use Composition over inheritance in Java. I have already mentioned about this design principle, in my list of 10 OOPS and SOLID design principles for Java programmers, here we will take a more closer look.

How to find CPU and Memory used by Java process in Solaris – prstat command example

2013-06-03T05:42:00.000-07:00

We often need to find CPU and memory utilization of a particular Java process in order to get some performance stats, capacity planning or just to understand the current load on system. Performance monitoring and testing is integral part of any Java application development, especially if you are working in high frequency trading space. In order to fix a performance problem, you have to find them first and knowledge of right tools and commands helps there. One of the primary cause of poor application performance be it Java or any other process is exhaustion of important resources like CPU and memory. Monitoring CPU and memory utilization of your Java process gives you some useful insight like what is normal memory and CPU utilization, when are you getting spikes on CPU and memory consumption. If heap memory is constantly increasing over time than it’s an indication that your Java application may have a memory leak. In this Java performance tutorial, we will learn about two most common Solaris commands prstat and pmap to find CPU and memory utilization of Java process. prstat is a process monitoring tool easily available in any Solaris systems including SPARC and x86 boxes, which provides useful statics of CPU and memory utilization of a process. For other systems e.g. windows you can use windows task manager for CPU monitoring and Linux you can use top command for same purpose. By the way, you can also check out Java performance by Charlie Hunt and BinuJohn, it is immensely helpful for Java performance monitoring and tuning. This is the book, which gives you right kind of tools and knowledge required to find performance stats for Java application.

How to Check if Integer Number is Power of Two in Java - 3 examples

2013-05-30T07:06:00.000-07:00

How to check if an integer number is power of 2 in Java is one of the popular programming interview question and has been asked in many interviews. Surprisingly, this problem which looks simple enough to answer, doesn't turn out that simple if for many developers. Many Java programmers, both freshers and less experienced, struggle to write code for a function, which can check if number is power of 2 or not. There could be many different reasons for that, but it’s expected to at least come up with brute force solution. For those who are familiar with bitwise operators in Java , how positive and negative numbers are represented in binary format, this exercise is quite easy. Since negative numbers are represented as 2's complement value in Java, you can easily find if any number is power of 2 or not by looking at its bit pattern. Remember checking for power of two is different than checking if number is even or odd, that’s another thing to note. A number can be even, but it’s not necessary to be a power of two, e.g. 6 is even but it’s not a power of two.

Java Tips and Best practices to avoid NullPointerException in Java Applications

2013-05-28T08:03:00.001-07:00

A NullPointerException in Java application is best way to solve it and that is also key to write robust programs which can work smoothly. As it said “prevention is better than cure”, same is true with nasty NullPointerException. Thankfully by applying some defensive coding techniques and following contract between multiple part of application, you can avoid NullPointerException in Java to a good extent. By the way this is the second post on NullPointerException in Javarevisited, In last post we have discussed about common cause of NullPointerException in Java and in this tutorial, we will learn some Java coding techniques and best practices, which can be used to avoid NullPointerException in Java. Following these Java tips also minimize number of !=null check, which litter lot of Java code. As an experience Java programmer, you may be aware of some of these techniques and already following it in your project, but for freshers and intermediate developers, this can be good learning. By the way, if you know any other Java tips to avoid NullPointerException and reduce null checks in Java, then please share with us.

Which Programming Book would you buy if you were given 100$ to spend?

2013-05-25T02:59:00.001-07:00

Hello Guys, it's time to take an hypothetical question in Javarevisited. Which programming book, would you love to buy, if you are given 100$ to spend? I know, when it comes to buying, people want to worth of there money, and that's why I am posting this question to you guys. Suppose you are looking some books in a bookstore and suddenly salesman comes and say, at this particular minute, we are giving you 100$ FREE to buy any programming book. Now you just have 10 minute to complete your purchase and take away those awesome Java books absolutely for FREE, what are the books you are going to buy?

10 XSLT or XML, XSL transformation Interview Questions and Answers for Java Programmers

2013-05-24T05:03:00.001-07:00

XSLT stands for XML style sheet transformation and it as XML technology used to transform one XML into another XML or HTML format. XML and XSLT interview questions are commonly asked to Java developers, who happen to use XML in there project and mentioned XSLT as key skill in there resume. Given XML’s popularity as data transfer protocol, many systems in middle and back office space uses XML messages to transfer trade details, for example Bookings, Settlement, and Confirmation system uses it as a data exchange protocol. Since each of this system performs some normalization, enrichment and transform on incoming trade message, they use XSLT for those transformation. XSLT is rich, powerful and given it’s support in Java and several other programming language, it comes natural choice of XML transformation. What you need to is to write XSL files, also known as XML style sheet to specify your transformation rule and than XSLT engine will transform each incoming XML documents as per your XSL file. Though, XSLT is rich, it’s can also be very complex for Java programmers, who are used to procedural style of coding, as XSLT uses recursion a lot. So if you are a Java programmer, who have used XSLT or going for a Job interview, where XSLT is a key skill, you better be prepare with some popular XSLT interview questions, In this article, I am sharing my list of XSLT questions, which is collected from internet, friends and colleagues and frequently asked as part of XML Interview questions.

SED Command Examples in UNIX and Linux, Find and Replace using Regular Expression

2013-05-20T05:52:00.003-07:00

SED command in UNIX is stands for stream editor and it can perform lot's of function on file like, searching, find and replace, insertion or deletion. Though most common use of SED command in UNIX is for substitution or for find and replace. By using SED you can edit files even without opening it, which is much quicker way to find and replace something in file, than first opening that file in VI Editor and then changing it. In this SED command tutorial we will see some practical examples of SED command in UNIX based systems e.g. Linux. I must say having a good grip on find, grep, sort, vi editor and SED can take you next level of UNIX and Linux working experience. These are very powerful UNIX command and helps with lot of different tasks in server. By the way we will use following text file for our SED common example. As I have said before, best way to learn any UNIX command is to use them in your day to day task, and a good example is a good start. This file contains details of some popular android and iPhone smartphones, e.g. Model, company, price etc, separated by colon. You can also use any CSV file for this example.