Monday, June 30, 2014

How to create Custom Exception in Java - Tutorial Example

Sometimes we need to create custom Exception in Java, i.e. Exceptions which are not defined in JDK or any third party library your application is using. Though it’s widely recommended on several Exception best practices article, even Joshua Bloch has recommended in Effective Java to prefer standard exception over custom exception, sometimes you really need it. There are certain guidelines to help to find whether you really need a custom exception or not. You should write your own exception classes if you answer yes to any of the following questions; otherwise, you can probably use someone else's.
  •     Do you need an exception type that isn't represented by those in the Java platform?
  •     Would it help users if they could differentiate your exceptions from those thrown by classes written by other vendors?
  •     Does your code throw more than one related exception?
  •     If you use someone else's exceptions, will users have access to those exceptions? The similar question is, should your package be independent and self-contained?

Thursday, June 26, 2014

How to use CopyOnWriteArraySet in Java with Example

CopyOnWriteArraySet is little brother of CopyOnWriteArrayList class. These are special purpose collection classes which was added on JDK 1.5, along with their most popular cousin ConcurrentHashMap. They are part of concurrent collection framework and reside in java.util.concurrent package. CopyOnWriteArraySet is best suited as read-only collection whose size is small enough to copy if some mutative operation happens, for example you can use CopyOnWriteArraySet to store object at start-up of application and let multiple application thread access them during application life time. If an new condition or object comes up during that time, it can also be added into this Set, with incurring cost of creating a new array.

Monday, June 23, 2014

20 Fancy Acronyms Programmers should know?

Do you read blogs on Internet? Do you understand what TL;DR or ITT means, Well I didn't, not until last year. Internet is full of acronyms. Techies, programmers, developers and bloggers has developed a lot more fancy acronyms than you can think of. If you participate or read articles on sites like Reddit, Hacker news or StackOverFlow, you will see extensive use of these mysterious acronyms. If you don't know meanings of acronyms like TL;DR, AFAIK, PSA, YSK or TIL, there is good chance that you will lost in conversation and comments. So when I come across this list of acronyms, I thought to share it with you guys. This list contains lots of popular acronyms, which is been used by many bloggers around internet and community web-sites like Reddit, Hacker News, DZone and StackOverFlow.

Tuesday, June 17, 2014

How to Count number of Set bits or 1's of Integer in Java?

There are multiple ways to count number of 1's or set bits in a integer number in Java. You can use bitwise and bit shift operator by your own, or, you can use Java API to count number of set bits. Java 1.5 added two utility method called bitCount(int i) which returns number of 1's in your integer number, java.lang.Long class has similar bitCount(long number) for long primitives. As I have said earlier, Coding questions are important part of any Java interview, and from that recursion and bitwise operations are most popular. Questions like, How to Swap two numbers without temp variable or How to find if a number is positive or negative are some of such questions, which you see now and then in various Java interviews.

Wednesday, June 11, 2014

Is Java Compiled or Interpreted Programming language?

One of the first question a graduate C or C++ programmer, who has just started learning Java ask is, whether Java is a compiled language or an interpreted one? On academic courses or during college, students learn a lot of languages e.g. VB, C, C++ and they happily categories them as either compiled or interpreted, but with Java it's tricky. It's not clear whether Java is compiled or interpreted, because it neither generate machine language code after compiling source file,  neither interpreted source file to execute instruction line by line. In order to answer this question you need to fist know that Java is a platform independent language? Which means you can run a Java program to any platform, which includes hardware + operating system, without any modification. Knowing how Java achieves platform independence is key to answer this question.

Monday, June 9, 2014

SynchronousQueue Example in Java - Produer Consumer Solution

SynchronousQueue is special kind of BlockingQueue in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa. When you call put() method on SynchronousQueue it blocks until another thread is there to take that element out of the Queue. Similarly, if a thread tries to remove an element and no element is currently present, that thread is blocked until another thread puts an element into the queue. You can correlated SynchronousQueue with athletes (threads) running with Olympic torch, they run with torch (object need to be passed) and passes it to other athlete waiting at other end.

Friday, June 6, 2014

Exception in thread "main" java.lang.ExceptionInInitializerError in Java Program

JVM throws java.lang.ExceptionInInitializerError, when there is an Exception inside static initializer block. If you know about static variable in Java, then you may know that they are initialized at the time of class loading. If there is an Exception during that initialization of static variables, you will see ExceptionInInitializerError in Java. This could be any exception e.g. java.lang.ArrayIndexOutOfBound or java.lang.NullPointerException. Java developers often confused with this error because, they think that they have not defined any static initializer block, then how come they are getting ExceptionInInitializerError; well, by default Java combines all static variable initialization inside a static initializer block and initialize them in the order they are declared in source file.

Tuesday, June 3, 2014

2 Examples to read Zip Files in Java, ZipFile vs ZipInputStream

ZIP format is one of the most popular compression mechanism in computer world. A Zip file may contains multiples files or folder in compressed format.  Java API provides extensive support to read Zip files, all classes related to zip file processing are located in package. One of the  most common task related to zip archive is to read a Zip file and display what entries it contains, and then extract them in a folder. In this tutorial we will learn how to do this task in Java. There are two ways you can iterate over all items in a given zip archive, you can use either or Since a Zip file contains several items, each of them has header field containing size of items in number of bytes. Which means you can iterate all entries without actually decompressing the zip file.