Kotlin’s features

msapps | January 21 / 2018 | Android

Kotlin is a Type Safety (statically typed) programming language developed by JetBrains, started in 2010 for modern multiplatform applications.
In 2011 JetBrains published a post “Why JetBrains need Kotlin”
The main topics were:
*To increase the productivity
Writing the IDEs in Java was taking a lot of time to compile with javac.
*To drive sales of IntelliJ IDEA
JetBrains wanted a programming language to be a part of IntelliJ IDEA, which will increase sales.
*Drive company’s business by keeping a trust
By developing a new programming language which will support other platforms, JetBrains wanted to increase the awareness and maintaining the community trust.
As it says in official Kotlin web site kotlinlang.org:
“Kotlin can be used for any kind of development, be it server-side, client-side web and Android. With Kotlin/Native currently in the works, support for other platforms such as embedded systems, macOS and iOS is coming.”
The benefits of learning Kotlin
There are many reasons to learn Kotlin:
  • Kotlin is an open source programming language.
  • It is 100% interoperable with Java and Android. In Google I/O 17 May 2017,
  • The Android team announced Kotlin as an official language for Android app development and it is fully compatible with JDK 6 and above.
  • Using Kotlin over Java will cut the number of code lines approximately by 40% which will decrease the number of errors (if there is less code, it’s more difficult for that code to fail).
  • Kotlin is many savers programming language than Java. It is aimed at removing the dangers of null references from the code.
Kotlin was influenced by Java, Scala, Groovy, C#, JavaScript and Gosu so it makes Kotlin easy to learn. Depends on FAQ at Kotline official web site, you can read and write Kotlin in a few days.
One of the major reasons to learn Kotlin is the fact that Kotlin climes to be a cross-platform language thanks to Kotlin/Native.
Kotlin/Native is a standalone compiler which compiles Kotline code directly to machine code with no dependency on any virtual machine.

“Our vision for inter-platform code reuse is the following:
one can write entire modules in Kotlin in a platform-independent way and compile them for any supported
platform (currently these are Kotlin/JVM, Kotlin/JS and the upcoming Kotlin/Native).”

Popularity of Kotlin
There is no doubt, Kotlin is the rising star of programming languages.
According to Tiobe.com, Kotlin ranking is 28 and it pretends for the programming language of the year. Kotlin was ranked 80th just in May this year.
There are many companies, using Kotlin these days. Companies like Pinterest, Square, Basecamp or Trello whose production code also includes some parts in Kotline.
Since Google announces Kotlin as an official language for Android app development, Kotlin became even more popular.
Well, only time will tell does Kotlin is really the next generation of programing language.
So why you should use Kotlin over Java?
As I mentioned before, Kotlin can reduce your code by 40% let’s take a quick view:

Below is an Example of POJO Class:

 public class Person {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Here is how it looks in Kotlin:

data class Person(val name: String)
Another and very useful feature is Extensions:
In Kotlin you can easily Extend a Function or a property without using inheritance:
 val n = 5
 n.sum(7) // will return a summarized value, in our case is 12


fun Int.sum(n: Int): Int {

        return this + n
    }
Kotlin Android Extensions how to use
This cool feature will free us from using the findViewById() function.
To use this coll feature please take a look at the example below:

Add this line to your app build.gradle file: apply plugin: ‘kotlin-android-extensions’ just below the ‘kotlin-android’ plugin
In MainActivity add this import import kotlinx.android.synthetic.main.activity_main.*
now you have in the class members of your XML TextView – Their name is just like their XML id
The code should look like

TextView
    android:id="@+id/helloView"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
import kotlinx.android.synthetic.main.activity_main.* … override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) helloView.setText(“Hello, world!”) }
Null Safty
In Java all variables store references to a memory address, except the primitive types. That’s why you can set it to Null and can throw  NullPointerException.
In Kotlin variables are non-null references by default unless otherwise defined.
For Example, a non-null variable will show a compile error if you will try to asign it to a null.
var mVar: String
mVar = null //Compiler error

However, if we need to assign a null to a variable, we must declare it explicitly by adding a-? right after the data type.

var mVar: String?
mVar = null //No error

Now, if we will try to use our variable we will receive a compile error

var mVar: String?

mVar.length   //compile error the varible can be null

To avoid the error we will have to add ? to the variable:

var mVar: String?

mVar?.length   // the type of mVar is null no error

One of my favorites usages of the Safe calls is using it in chains. For example:

person?.name?.length

This code will return null if one of the properties is null.

Elvis Operator
var z: String? // Nullable value

Now z can be null. Let’s say we need to perform a safety check, whether z contains a value or its null.
In Java we will use if…esle

 String z = null;
 int a = (z != null) ? z.length() : -1;

Or in Kotlin

var z: String? = null
 val a: Int = if (z != null) z.length else -1

Kotlin Elvis operator is the short equivalent version for the if…else statement

val a = z?.lengh ?: -1
The !! Operator
val a = z!!.length

In case we will need the NPE, we can always get it explicitly by adding !! to our variable

When Expression
When expression in Kotlin is the new switch case:
        when (a){
            1 -> Log.i(TAG, "The value is: 1")
            2 -> Log.i(TAG, "The value is: 2")
            in 3..5 -> Log.i(TAG, "The value is: $a")
            else -> Log.i(TAG, "The value is bigger then 5")
        }

Using when for checking a variable type

    when (a){
            is Int -> Log.i(TAG, "The value is Int")
            is String ->  Log.i(TAG, "The value is String")
            is Double ->  Log.i(TAG, "The value is Double")
        }
Equals
In Kotlin we will use == instead of equals
In Java, the == operator is used for compare references and in Kotline we are using the == operator to compare data or variables.
  val mike = Person("John")
  val john = Person("John")
  
  mike == john    // true  (structural equality)
  mike === john   // false (referential equality)
Lambdas in Kotlin

Lambda expression in computer programming, also called anonymous function, a function (or a subroutine) defined, and possibly called, without being bound to an identifier

val multi = {a: Int, z: Int -> a * z}
val val = multi(5, 7)

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