Kotlin is a statically typed programming language that runs on the Java Virtual Machine (JVM). It was developed by JetBrains and officially released in 2016. Kotlin is designed to interoperate fully with Java, allowing developers to use Kotlin and Java seamlessly within the same project. This interoperability means that Kotlin can use Java libraries, frameworks, and tools, and vice versa. Moreover, existing Java code can be called from Kotlin and Kotlin code can be used in Java, making it an attractive option for developers looking to leverage the vast ecosystem of Java while benefiting from Kotlin's modern features and more concise syntax.

Kotlin addresses many of the shortcomings of Java, such as null pointer exceptions and verbose syntax. It introduces many features that Java lacks, including null safety, extension functions, coroutines for asynchronous programming, data classes, and type inference, making the code more concise and expressive.

Despite these improvements, Kotlin maintains a low learning curve for Java developers due to its similar syntax and interoperability. This has led to Kotlin being adopted by a wide range of developers and companies, and it was even named an official development language for Android by Google in 2017. Kotlin's design goals include enhancing productivity, improving code safety, and increasing developer happiness, making it a popular choice for new projects.

Things that make Kotlin better than Java

Kotlin introduces several features and improvements over Java, making it more concise, expressive, and safer. Here are some examples where Kotlin provides a more efficient or cleaner approach compared to Java:

1. Null Safety

• Java: Prone to null pointer exceptions. Developers must manually check if an object is null to avoid runtime exceptions.
• Kotlin: Built-in null safety through nullable and non-nullable types. Trying to assign or return null to a non-nullable type will result in a compile-time error.

// Kotlin
var a: String = "abc"
// a = null // Compilation error
var b: String? = "xyz" // Nullable type
b = null // Allowed

2. Data Classes

• Java: Requires boilerplate code for data classes (e.g., getters, setters, equals(), hashCode(), toString()).
• Kotlin: Provides a data keyword to automatically generate all the boilerplate code for data handling methods.

// Kotlin
data class User(val name: String, val age: Int)

3. Extension Functions

• Java: Requires utility classes or methods to add functionality to existing classes.
• Kotlin: Allows adding new functions to any class without inheritance or decoration.

// Kotlin
fun String.addExclamation() = this + "!"

val greeting = "Hi"
println(greeting.addExclamation()) // Prints: Hi!

4. Default and Named Arguments

• Java: Overloading methods for different scenarios or manually handling default values.
• Kotlin: Supports default arguments and named parameters, reducing the need for method overloads.

// Kotlin
fun buildMessage(greeting: String, name: String = "Guest") = "$greeting, $name!"

println(buildMessage("Hello", "Alice")) // Prints: Hello, Alice!
println(buildMessage("Welcome")) // Uses default name. Prints: Welcome, Guest!

5. Coroutines for Asynchronous Programming

• Java: Relies on complex callback patterns or future/promises for asynchronous programming, which can lead to callback hell.
• Kotlin: Offers coroutines as a built-in feature, simplifying asynchronous programming and making code more readable and easier to write.

// Kotlin Coroutine Example
suspend fun fetchData(): Data {
    return withContext(Dispatchers.IO) {
        // Simulate long-running operation
        // Return data
    }
}

6. Smart Casts

• Java: Requires explicit casting even after an instanceof check.
• Kotlin: Automatically casts variables after type checks, eliminating the need for explicit casting.

// Kotlin
if (obj is String) {
    // obj is automatically cast to String here
    println(obj.length)
}

7. Type Inference

• Java: Often requires explicit type declarations.
• Kotlin: Has powerful type inference, allowing you to omit the type when it can be inferred by the compiler, making the code cleaner and more readable.

// Kotlin
val message = "Hello World" // Type String is inferred

These examples illustrate how Kotlin provides more concise, expressive, and safer alternatives to common Java patterns, enhancing developer productivity and code maintainability.