Kotlin : Basics (Post 2)

Hi All ,

Previously , I posted the overview of Kotlin . Kotlin is fully supported in Android Studio 3.0 and higher. 
For Kotlin support , we just need to select the Kotlin language , at the time of configure the new android project in Android Studio. 
Now let's take a look at some basics of Kotlin Language :

=> Declare Variables :

val and var both are used to declare a variable. var is like general variable and it's known as a mutable variable in kotlin and can be assigned multiple times.val is like Final variable and it's known as immutable in kotlin and can be initialized only single time.

=>Numbers : 

The representation of numbers in Kotlin is pretty similar to Java, however, Kotlin does not allow internal conversion of different data types. Here is one example of my Demo Activity :

class MainActivity : AppCompatActivity() {

    val intergerValue: Int = 10    

    val doubleValue: Double = 10.00   

    val floatValue: Float = 10.00f
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        println("Int Value is "+intergerValue)
        println("Double  Value with string is -> $doubleValue ");
        println("Float Value is "+floatValue)
    }

}

 Output: 

Int Value is 10
Double  Value with string is -> 10.0 
Float Value is 10.0

Explanation :
Here in this example , we can see that , in second print statement , I have used semicolon(;), at the end of statement . Semicolon (;) is not mandatory at the end of statement in Kotlin.

Another thing , I have used $ , to print the value of variable within the String . Otherwise , we can used + size to append the value with String (same as JAVA).

=> Characters & Boolean : 

Assigning and defining of character and boolean variables should be done like this :

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    val letter: Char    // defining a variable 
    letter = 'R'        // Assigning a value to it 
    println("$letter")
   
    val letter1: Boolean   // defining a variable 
    letter1 = true         // Assinging a value to it 

    println("Character value -> "+"$letter1")
}

  Output: 

R
Character value -> true

Explanation: 

Here ,  we can not reassign any new value for that "val" variable .It will throw compile time error: 

"Val value can not be reassigned! "

=> String :


 var rawString :String ="I am Raw String!\n" 

 println("Hey!!"+rawString) 



  Output: 

Hey!!I am Raw String!



=> Arrays :

Arrays should be defined like following :

var Arr1 = arrayOf(1,10,4,6,15)
var Arr2 = arrayOf<Int>(1,10,4,6,15)
var Arr3 = arrayOf<String>("Surat","Mumbai","Rajkot")
var Arr4 = arrayOf(1,10,4, "Ajay","Prakesh")
var Arr5: IntArray = intArrayOf(5,10,15,20)

println("Hey!! I am array Example1->"+Arr1[2])
println("Hey!! I am array Example2->"+Arr2[2])
println("Hey!! I am array Example3->"+Arr3[2])
println("Hey!! I am array Example4->"+Arr4[3])
println("Hey!! I am array Example5->"+Arr5[2])




Output: 
Hey!! I am array Example1->4
Hey!! I am array Example2->4
Hey!! I am array Example3->Rajkot
Hey!! I am array Example4->Ajay
Hey!! I am array Example5->15
Explanation: 
Here , in Arr4 , we can see that we can also define , integer and String in one array also.


=> ArrayList :

 val arrayList = ArrayList<String>()

  arrayList.add("Hello")
  arrayList.add("Hi")
  arrayList.add("Good Morning")
  println("Size of ArrayList->"+arrayList.size)

Output: Size of ArrayList->3

That's it , for this post . In next post we will go through the condition statements and control flows.