fun result(args: Array<String>) =
  html {
    head {
      title {+"XML encoding with Kotlin"}
    }
    body {
      h1 {+"XML encoding with Kotlin"}
      p  {+"this format can be used as an alternative markup to XML"}

      // an element with attributes and text content
      a(href = "http://kotlinlang.org") {+"Kotlin"}

      // mixed content
      p {
        +"This is some"
        b {+"mixed"}
        +"text. For more see the"
        a(href = "http://kotlinlang.org") {+"Kotlin"}
        +"project"
      }

      // content generated by
      p {
        for (arg in args)
          +arg
      }
    }
  }
					

  
    
  
  
    

      XML encoding with Kotlin
    
    

      this format can be used as an alternative markup to XML
    
    
      Kotlin
    
    

      This is some
      
        mixed
      
      text. For more see the
      
        Kotlin
      
      project
    
    

      some text
    
    

    
  

					

Kotlin

A powerful new language for the JVM

Erwin de Gier | Software Architect | Open Source

Today's goal

“To get you to start with Kotlin in your project this Monday!”

What is Kotlin?

Why Kotlin?

• Compact, concise syntax
• Powerful features like type inference, higher order functions, Null safety, named parameters, extension functions
• 100% Java compatible, 100% open source
• Java 6 (think your current project or Android)

public class Person {
    private  String firstName;
    private  String lastName;
    private  LocalDate birthDay;

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public LocalDate getBirthDay() {
        return birthDay;
    }

    public void setBirthDay(LocalDate birthDay) {
        this.birthDay = birthDay;
    }


    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Person person = (Person) o;

        if (firstName != null ? !firstName.equals(person.firstName) : person.firstName != null) return false;
        if (lastName != null ? !lastName.equals(person.lastName) : person.lastName != null) return false;
        return birthDay != null ? birthDay.equals(person.birthDay) : person.birthDay == null;

    }

    @Override
    public int hashCode() {
        int result = firstName != null ? firstName.hashCode() : 0;
        result = 31 * result + (lastName != null ? lastName.hashCode() : 0);
        result = 31 * result + (birthDay != null ? birthDay.hashCode() : 0);
        return result;
    }

    @Override
    public String toString() {
        return "Person{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", birthDay=" + birthDay +
                '}';
    }
}
					

data class Person(var firstName : String, var lastName : String, var birthDay : LocalDate)
					

Basics

• Functions can exists on file level
• Classes do not have to be in their own file

fun main(args: Array<String>) {
   println("Hello World")
}
					

fun main(args: Array<String>) : Unit {
	val total = { x: Int, y: Int -> x + y}  //lambda statement
	println(total(1,2));		//calling a function by variable name
	println("Hello, World")
	
	val list = listOf(-2,-1,0,1,2)
	list.filter { it > 0 }.forEach { println(it) }   //functions on iterables

	val sum = ::calculateTotal   //function reference
	println(sum(2,2)) //prints 4
}

fun calculateTotal(x: Int, y: Int) = x + y //Example of an inline function, 
//where the curly braces, return type and return statement can be ommitted.

fun closure() {
	val list = listOf(-2,-1,0,1,2)
	var total = 0;
	list.filter { it > 0 }.forEach { 
		total += it  //mutable accessibility to the variables in the "closure"
	}
	println(total) //prints 3
}

fun types() {
	val s = "ABC"  //type inference
	var i = 1
	var i2: Int = 1   //explicit typing
	if(i is Int){
		println("i is of type Int")  //type check
	}
	var text: String? = null    //nullable types
	println(text?.length)
}
						
					

fun createPerson = createPerson(lastName = "lastname", height = 1.82)  
//named /optional parameters
fun createPerson(firstName: String = "", lastName: String = "", street: String = "", number: Int = 0, height: Double = 0.0) {
	
}

fun whenExample(x : Int){ 
	val result = when(x) {
		getValue(x) -> print("getValue")
		0,1 -> print("0 or 1")
		else -> print("else")
	}
	//when with smart casts
	val y : Any = ""
	when(y) {
		is String -> print(y.length)
		is Int -> print(y.minus(1))
		else -> print("else")
	}

}



//extension function
fun String.allUpperCase() : Boolean {
		return this == this.toUpperCase()
}
						
					

Getting Started

• IntelliJ: congrats, your done!
• Eclipse: install the Kotlin plugin
• git clone https://github.com/erwindeg/kotlin-koans

Kotlin Koans 1 Introduction

“Let's write some code!”

testScript {
	post("/user/", params("email" to "erwin@edegier.nl","firstname" to "Erwin","lastname" to "de Gier")){
		expectedResult("OK")
	}
	get("/user/erwin"){
		expectedResult(params("email" to "erwin@edegier.nl","firstname" to "Erwin","lastname" to "de Gier"))
	}	
}

fun testScript(init : TestScript.() -> Unit ) : TestScript {
	val testScript = TestScript()
	testScript.init();
	return testScript;
}

class TestScript {
	fun get(url: String, params: Map<String,String> = mapOf(), validate : RestCall.() -> Unit) : RestCall  {
		var call = RestCall(Method.GET,url,params)
		call.performCall()
		call.validate()
		return call
	}
 	...
}
					

Kotlin Koans 5 Builders

“Let's write some code!”

Kotlin and Java project

https://github.com/erwindeg/kotlin-example

|kotlin-java
|-pom.xml //Kotlin compiler, kotlin stdlib, kotlin test 
|-src/main/java //Kotlin and Java classes
|-src/test/java //Kotlin and Java tests
					

What's next?

Continue with the Koans from II

Read the reference

https://kotlinlang.org/docs/kotlin-docs.pdf