sliskiCode

import lombok.Builder;

@Builder
class Person {
    private final String name;
    private final String surname;
    private final int age;
}

sliskiCode

class Person(val name: String, val surname: String, val age: Int) {
    companion object {
        class Builder {
            private var name: String = ""
            private var surname: String = ""
            private var age: Int = 0

            fun name(name: String): Builder {
                this.name = name
                return this

sliskiCode

class Person private constructor(val name: String, val surname: String, val age: Int) {

    private constructor(builder: Builder) : this(builder.name, builder.surname, builder.age)

    companion object {
        fun create(init: Builder.() -> Unit) = Builder(init).build()
    }

    class Builder private constructor() {

sliskiCode

fun main(args: Array<String>) {
    measureTime {
        Person.create {
            name { "Peter" }
            surname { "Slesarew" }
            age { 28 }
        }
    }

    // OR

sliskiCode

val withTitle: Boolean = true

// More concise
Person.create {
    name { if (withTitle) "Mr. Peter" else "Peter" }
    surname { "Slesarew" }
    age { 28 }
}

// It does not even compile

sliskiCode

class Person(val name: String, val surname: String, val age: Int = 0)

Person(name = "Peter", surname = "Slesarew") // <- name, surname are mandatory
Person(name = "Peter") // <- it does not compile
Person(surname = "Slesarew") // <- it does not compile
Person(age = 28) // <- it does not compile

sliskiCode

class CopyPrinter implements Copy, Print {

    private Copy copier;
    private Print printer;

    public CopyPrinter(Copy copier, Print printer) {
        this.copier = copier;
        this.printer = printer;
    }

sliskiCode

class CopyPrinter(copier: Copy, printer: Print) : Copy by copier, Print by printer

interface Copy {
    fun copy(page: Page): Page
}

interface Print {
    fun print(page: Page)
}

sliskiCode

public final class CopyPrinter implements Copy, Print {
   // $FF: synthetic field
   private final Copy $$delegate_0;
   // $FF: synthetic field
   private final Print $$delegate_1;

   public CopyPrinter(@NotNull Copy copier, @NotNull Print printer) {
      Intrinsics.checkParameterIsNotNull(copier, "copier");
      Intrinsics.checkParameterIsNotNull(printer, "printer");
      super();

sliskiCode

import org.junit.Assert.assertEquals
import org.junit.Test

fun String.removeWhitespaces() = replace(" ", "")

class StringKtTest {
    @Test fun removesWhitespacesFromString() {
        val tested = "Piotr Slesarew"

        val actual = tested.removeWhitespaces()