Kotlin

Kotlin started at JetBrains. The syntax is shorter than Java, and the type shows null danger. A Java library can be called from Kotlin. It also runs on a server with Ktor or Spring, but the widest place is Android.

Kotlin is used in a new Android app and to shorten a Java project.

• An Android screen and its logic
• Replacing a Java class step by step
• A server API
• Shared mobile code

With Kotlin you write an Activity or a Compose screen, a list, and a network call. A data class replaces a long Java POJO. A Kotlin file can sit beside a Java file without deleting it.

Someone who knows Java reads it quickly. The difficulty is the null system, coroutines, and mixing them with Android’s own lifetime. The language is easy in a small sample and middling in an app’s architecture.

Advantage: short code, null checks, and living next to Java. Limit: the build can be slower than Java, and a misused coroutine mixes up the flow. Old Android samples are still in Java.

val is a value that does not change. var can change. A type with ? may be null. A data class creates equality and a copy.

• fun opens a function
• A coroutine waits for a long job without blocking
• The Gradle Kotlin DSL describes the build
• A Java file and a Kotlin file can share a module

This program writes one line from the main function.

fun main() {
    println("Hello")
}

• Does Kotlin delete Java? No. Java libraries stay. New code is often Kotlin.
• Is Kotlin only for Android? No. It also runs on a server.
• Is it the same as Swift? No. Swift is for Apple. Kotlin is for the JVM and Android.