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Thursday, May 28, 2015

How to Convert Byte array to String in Java with Example

There are multiple ways to convert a byte array to String in Java but most straight forward way is to use the String constructor which accepts a byte array i.e. new String(byte []) , but key thing to remember is character encoding. Since bytes are binary data but String is character data, its very important to know the original character encoding of the text from which byte array has created. If you use a different character encoding, you will not get the original String back. For example, if you have read that byte array from a file which was encoded in "ISO-8859-1" and you have not provided any character encoding while converting byte array to String using new String() constructor then its not guaranteed that you will get the same text back? Why? because new String() by default uses platform's default encoding (e.g. Linux machine where your JVM is running), which could be different than "ISO-8859-1". If its different you may see some garbage characters or even different characters changing the meaning of text completely and I am not saying this by reading few books, but I have faced this issue in one of my project where we are reading data from database which contains some french characters. In the absent of any specified coding, our platform was defaulted on something which is not able to convert all those special character properly, I don't remember exact encoding. That issue was solved by providing "UTF-8" as character encoding while converting byte array to String. Yes, there is another overloaded constructor in String class which accepts character encoding i.e. new String(byte[], "character encoding").

Tuesday, May 26, 2015

4 ways to concatenate Strings in Java - Best Performance

When we think about String Concatenation in Java, what comes in our mind is + operator, one of the easiest way to join two String, or a String and a numeric in Java. Since Java doesn't support operator overloading, it's pretty special for String to have behavior. But in truth, it is the worst way of concatenating String in Java. When you concatenate two String using + operator e.g. "" + 101, one of the popular way to convert int to String, compiler internally translate that to StringBuilder append call, which result in allocation of temporary objects. You can see the real difference in performance of our example program, in which we have concatenated 100,000 String using + operator. Anyway, this article is not just about + operator but also about other ways to concatenate multiple Strings. There are four ways to do this, apart from + operator, we can use StringBuffer, StringBuilder and concat() method from java.lang.String class for same purpose. StringBuilder and StringBuffer classes are there for just this reason, and you can see that in our performance comparison. StringBuilder is winner and fastest ways to concatenate Strings. StringBuffer is close second, because of synchronized method and rest of them are just 1000 times slower than them. Here we will see example of all four ways of concatenating Strings in Java.

Sunday, May 24, 2015

Difference between Abstraction and Polymorphism in Java OOPS

Abstraction and Polymorphism are very closely related and understanding difference between them is not as easy as it looks. Their operating model is also similar and based upon relationship between parent and child class. In fact, Polymoprhism needs great support of Abstraction to power itself, without Abstraction you cannot leverage power of Polymorphism. Let's understand this by what Abstraction and Polymorphism provides to an object oriented program. Abstraction is a concept to simplify structure of your code. Abstraction allows you to view things in more general terms rather than looking them as they are at the moment, which gives your code flexibility to deal with the changes coming in future. For example, if you were to design a program to control vehicles e.g. starting, stopping, horn, accelerator, breaks etc, how do you do that? would you design your program just to work with car or bike or would you think about different kinds of vehicles? This is where Abstraction comes into picture, it allows you think in terms of Vehicle rather than thinking in terms of Car. It provide that generalization much needed for a software to be reusable and customizable.