Kotlin is a statically typed JVM language that enables code that is expressive, short, and readable. Spring framework 5.0 has good support for Kotlin.

Consider a simple Kotlin program illustrating a data class, as shown here:

    import java.util.*
    data class Todo(var description: String, var name: String, var  
    targetDate : Date)
    fun main(args: Array<String>) {
      var todo = Todo("Learn Spring Boot", "Jack", Date())
      println(todo)
        //Todo(description=Learn Spring Boot, name=Jack, 
        //targetDate=Mon May 22 04:26:22 UTC 2017)
      var todo2 = todo.copy(name = "Jill")
      println(todo2)
         //Todo(description=Learn Spring Boot, name=Jill, 
         //targetDate=Mon May 22 04:26:22 UTC 2017)
      var todo3 = todo.copy()
      println(todo3.equals(todo)) //true
    }  

In fewer than 10 lines of code, we created and tested a data bean with three properties and the following functions:

• equals()
• hashCode()
• toString()
• copy()

Kotlin is strongly typed. But there is no need to specify the type of each variable explicitly:

    val arrayList = arrayListOf("Item1", "Item2", "Item3") 
    // Type is ArrayList

Named arguments allow you to specify the names of arguments when calling methods, resulting in more readable code:

    var todo = Todo(description = "Learn Spring Boot", 
    name = "Jack", targetDate = Date())

Kotlin makes functional programming simpler by providing default variables (it) and methods such as take, drop, and so on:

    var first3TodosOfJack = students.filter { it.name == "Jack"   
     }.take(3)

You can also specify default values for arguments in Kotlin:

    import java.util.*
    data class Todo(var description: String, var name: String, var
    targetDate : Date = Date())
    fun main(args: Array<String>) {
      var todo = Todo(description = "Learn Spring Boot", name = "Jack")
    }

With all its features making the code concise and expressive, we expect Kotlin to be a language to be learned for the .

We will discuss more about Kotlin in Chapter 13, Working with Kotlin in Spring.