Kotlin Introduction, Environment Setup, Syntax, and Java Interoperability

This article provides a comprehensive introduction to Kotlin, covering its origins, key features, and advantages over Java, followed by detailed instructions for setting up the development environment in IntelliJ IDEA, Android Studio, Eclipse, and online playgrounds.

It explains how to configure Gradle build files for Kotlin projects, including the necessary plugins and dependencies:

buildscript {
    ext.kotlin_version = '1.1.2-5'
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}
apply plugin: 'kotlin-android'

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
}

The core Kotlin syntax is presented, including variables (val/var) with type inference, functions (block‑body and expression‑body), top‑level functions, extension functions, higher‑order functions, control structures (when, for, while), collections, interfaces with default implementations, classes, abstract classes, primary and secondary constructors, data classes, and the object keyword.

Examples of variable declaration and function definitions:

val answer: Int = 42
val answer = 42 // type inference

fun max(a: Int, b: Int): Int = if (a > b) a else b

Extension function example:

fun String.lastChar(): Char = get(length - 1)

Higher‑order function example for SharedPreferences:

fun SharedPreferences.editor(f: (SharedPreferences.Editor) -> Unit) {
    val editor = edit()
    f(editor)
    editor.apply()
}

Interoperability between Kotlin and Java is demonstrated with examples of calling Kotlin from Java and vice‑versa, handling null‑safety, platform types, and using @JvmOverloads for overloads:

// Kotlin calling Java
val data = DataClass()
data.id = 0
println(data.id)

// Java calling Kotlin
User user = new User("abc", true);
user.getNickname();
user.isOpen();

Finally, the article introduces the Anko library for Android development, showing how to add it via Gradle and providing a DSL layout example:

dependencies {
    compile "org.jetbrains.anko:anko:$anko_version"
    // or specific modules
    compile "org.jetbrains.anko:anko-commons:$anko_version"
    compile "org.jetbrains.anko:anko-sdk25:$anko_version"
}

verticalLayout {
    val email = editText { hint = "Email" }
    val password = editText {
        hint = "Password"
        transformationMethod = PasswordTransformationMethod.getInstance()
    }
    button("LogIn") {
        onClick { logIn(email.text, password.text) }
    }
}

The article concludes with references to official Kotlin documentation, the Kotlin GitHub repository, and additional learning resources.