Tutorials
4 posts
Jun 26 2019
Reasons to choose Kotlin
Hello there! My name is Divyansh Jain. I am a student of Mahatma Jyoti Rao Phoole University. I have been selected as the Android developer for the XWiki organization and I am working on their XWiki Android Authenticator application in GSOC19.
XWiki android Authenticator aims to integrate a wiki instance in Android accounts, mainly including the synchronization of contacts and the XWiki authenticator. By synchronizing contacts of your company on your phone, it becomes easier to communicate and collaborate with each other.
Ever since the start of my work on the XWiki Android Authenticator app, I have been constantly learning new things. In the first week, I migrated most of the XWiki Android Application code from Java to Kotlin. And on this page, I would like to share my understanding of Kotlin that I have gained so far.
Getting started with Kotlin
Kotlin is officially supported by Google for mobile development on Android. It was released in Android Studio 3.0 on October 2017. At first, I was a bit afraid to switch to Kotlin since I feared that the code might crash and not run properly, but as I read the documentation, I started understanding the nuances of the language which made the switch from Java to Kotlin an easier process. I started realizing the advantages of Kotlin over Java. Some of them being:
Java Interoperability
I started with migrating the whole XWiki Android Authenticator app code from Java to Kotlin. I was replacing one Java file at a time, and while migrating I saw that Kotlin worked with Java smoothly. Though it required some direct imports, there were no errors in running the app on the device.
Changed variable declaration
In Java, we declare string for instance, String str = "Hello";.
In Kotlin, we declare string for instance, val str = "Hello" or val str: String = "Hello". Here val declares a read-only property or local variable whereas var declares a mutable property or local variable.
The final keyword is default in class
In Kotlin final is a default. E.g.
class Button {
fun click() = print("Click")
}
class displayToast : Button() { // Error
override fun click() = print("Toast Displayed") // Error
}
In the above example, class displayToast can’t inherit Button class because it is final. Moreover, it can’t override click(), because it is final in Button.
open fun click() = print("Click")
fun doubleClick() = print("Double Click")
}
class displayToast () : Button { // Inheritance is now possible
override fun click() = print("Toast Displayed") // Now it works
override fun displayToast () = print("Toast Displayed") // Error
}
In order to inherit and override, we put “open” keyword that allows inheritance and overriding.
Fun keyword for defining functions
Now in Kotlin, there is a new way to define functions. E.g.
fun addDigitis (a: int, b: int) : String { } //with arguments inside function
It is same as the Java parameterized method or empty method.
The when expression
The "switch-case" is replaced with the much more readable and flexible "when" expression: E.g.
when (x) {
1 -> print("x is 1")
2 -> print("x is 2")
3, 4 -> print("x is 3 or 4")
in 5..10 -> print("x is 5, 6, 7, 8, 9, or 10")
else -> print("x is out of range")
}
It works without the argument too.
Static keywords
For declaring static methods & variables, you can put them above the class name, then you can use them by importing directly in other classes.
Null Safety
One of the biggest flaws in Java is the way it handles “null,” leading to the dreaded NulPointerException (NPE). Kotlin resolves this by distinguishing between non-null types and nullable types. Types are non-null by default, and can be made nullable by adding a safe call ‘?’. E.g.
a = null // compile error
var b: String? = "xyz"
b = null // no problem
Conclusion
So after seeing, reading and migrating the code from Java to Kotlin, in my honest opinion, I do not see any reason to not choose Kotlin over Java. For instance, we need to write less code as compared to Java, we don't have to face the dreaded ‘NPE’ error anymore, interoperability with existing Java files, smart casts while declaring variables and many more. We've given the fair amount of our time to Java, but it's time to let it go and welcome our new friend Kotlin.
Happy Reading.
Jul 14 2016
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Use the Apache HTTP library to interact with the XWiki RESTful API
XWiki provides fine-grain access to virtually every element through an API that is based on HTTP semantics, i.e., a RESTful API. In this post you will find all the details to take advantage of this API and interact with it from Java or Groovy using Apache HttpComponents 4.x. ...
