What key features distinguish Kotlin from Java?

Coroutines, extensions, null safety, data classes, more concise syntax for many constructs (e.g., lambda expressions, conditional operators, iterations).

Feature	Kotlin	Java
Null Safety	Built-in support at the type system level.	Can result in NullPointerException at runtime.
Extensions	Ability to add new functions to existing types without inheritance.	No direct support.
Coroutines	Lightweight threads for asynchronous programming.	Traditional heavy threads (or third-party libraries like Project Loom).
Data Classes	Automatically generate equals(), hashCode(), toString(), copy().	Must be implemented manually (or use Lombok).
Smart Casts	Compiler automatically performs type casting after type checks.	Requires explicit casting.
Lambda Expressions	More concise syntax.	More verbose syntax.
Nested Classes	Inner classes are nested by default (nested).	Inner classes are inner by default (inner).
Mutable/Immutable	Separation of collections into mutable and immutable.	No explicit separation in the collection type system.
Operator Overloading	Support for operator overloading.	No support.

// Example of a data class
data class User(val name: String, val age: Int)

// Example of an extension function
fun String.addExclamation(): String = this + "!"

// Example of null safety
var nullableString: String? = null
// nullableString.length // Compilation error if not checked

// Example of a coroutine
import kotlinx.coroutines.*

fun main() = runBlocking {
    launch { // Launches a new coroutine and continues
        delay(1000L) // Non-blocking delay of 1 second (default time unit is ms)
        println("World!")
    }
    println("Hello") // Main coroutine continues while child is running
}

// Equivalent of a data class in Java (without Lombok)
public class User {
    private final String name;
    private final int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }

    // Manual implementation of equals(), hashCode(), toString() needed
}

// NullPointerException in Java
String nullableString = null;
// int length = nullableString.length(); // Runtime Exception: NullPointerException