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fun MutableList<Int>.swap(index1:Int,index2:Int){

       val tmp=this[index1]

       this[index1]=this[index2]

       this[index2]=tmp

       } 

goindwalia

val book = Book(“Kotlin”, “JetBrains”)
	
val copy = book.copy()

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/* 	kotlin Code */
	
	data class Book(var title:String,var author:Author)

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/* 	Java Code 	*/
	
class Book {

   private String title;

   private Author author;
  
   public String getTitle() {

goindwalia

/* 	Kotlin Program */

data class Address(var street:String,

       var streetNumber:Int,

       var postCode:String,

       var city:String,

goindwalia

/* 	Java program */	

public class Address {
  
   private String street;

   private int streetNumber;

   private String postCode;

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/* won’t compile */	
  val name: String? = null
  val len = name.length	

/* correct way */	
  val name: String? = null	
  val len = name?.length

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val name: String? = null	 	 //assigned 	null and it will compile 	also.
	
fun getName() : String? = null	//returned null and it 	will compile too.

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val 	name: String = null 	// tries to assign null, won’t 	compile.
	
fun 	getName() : String = null 	// tries to return null, won’t 	compile.

goindwalia

/* Kotlin Code*/
/* Simple Hello Word Example*/

//optional package header
package hello 

//package level function, which return Unit and takes an array of string as parameter
fun main(args: Array < String > ) { 
 val scope = “world”
 println(“Hello, $scope!”) //semicolons are optional, have you noticed that? :)