Kotlin vs Java: Why developers are massively switching to Kotlin

📚 Brief history

Java appeared in 1995 and for a long time was the standard for Android development and enterprise applications. However, the language began to show its age: verbose syntax, lack of modern capabilities, slow development.

Kotlin developed by JetBrains in 2011. The language was originally created as a modern alternative to Java, fully compatible with Java code. In 2017, Google officially added Kotlin support to Android Studio, and in 2019 made it a priority language for Android.

🚀 Key benefits of Kotlin

1. Code conciseness

Kotlin allows you to write less code to solve the same problems.

public class User {
    private String name;
    private int age;
    
    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public int getAge() {
        return age;
    }
    
    public void setAge(int age) {
        this.age = age;
    }
}

data class User(
    var name: String, 
    var age: Int
)

⚡ Result

Only one line instead of 20+! Kotlin automatically generates getters, setters, equals(), hashCode(), and toString().

2. Null Safety — safety from NullPointerException

NullPointerException is one of the most common errors in Java. Kotlin solves this problem at the language level.

String name = user.getName();
int length = name.length(); 
// May fall with NullPointerException!

val name: String? = user.name 
// ? means that it can be nullval length = name?.length ?: 0
// Safe handling

In Kotlin, you explicitly specify whether a variable can be null. The compiler will not let you forget about the check.

3. Extension functions

Kotlin allows you to add new methods to existing classes without inheritance.

// Add the method to the Stringfun String.removeSpaces() class: String {
    return this.replace(" ", "")
}

// Using val text = "Hello World"val result = text.removeSpaces() // "HelloWorld"

In Java, this would require creating utility classes.

4. Coroutines for asynchrony

Working with asynchronous code in Java has always been a pain. Kotlin offers coroutines - lightweight streams that make asynchronous code simple and readable.

networkCall(new Callback() {
    @Override
    public void onSuccess(Result result) {
        databaseSave(result, new Callback() {
            @Override
            public void onSuccess() {
                updateUI();
            }
        });
    }
});

suspend fun loadData() {
    val result = networkCall()
    databaseSave(result)
    updateUI()
}

💡 The magic of coroutines

The code looks synchronous, but it works asynchronously! No callback hell and complex chains.

5. Smart typecasting

fun processValue(value: Any) {
    if (value is String) {
        // Kotlin automatically converts value to String
        println(value.length)
    }
}

In Java, you would have to do an explicit type conversion: (String) value.

6. Default values and named parameters

fun createUser(
    name: String,
    age: Int = 18,
    city: String = "Moscow"
) {
    // ...
}

// Call with different combinations of parameters createUser("Alexey")createUser("Maria", age = 25)
createUser("Ivan", city = "St. Petersburg", age = 30)

This eliminates the need to create many overloaded methods, as in Java.

📱 Kotlin in Android development

Example of a simple screen in Jetpack Compose:

@Composablefun GreetingScreen(name: String) {
    Column(
        modifier = Modifier.fillMaxSize(),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        Text(
            text = "Hi, $name!",
            style = MaterialTheme.typography.h4
        )
        Spacer(modifier = Modifier.height(16.dp))
        Button(onClick = { /* действие */ }) {
            Text("Click me")
        }
    }
}

🖥️ Kotlin in server development

Kotlin is not limited to mobile development. It is actively used on the server:

Spring Framework

Spring is the most popular Java framework for server development, now fully supports Kotlin.

@RestController@RequestMapping("/api/users")
class UserController(private val userService: UserService) {
    
    @GetMapping("/{id}")
    fun getUser(@PathVariable id: Long): User? {
        return userService.findById(id)
    }
    
    @PostMapping
    fun createUser(@RequestBody user: User): User {
        return userService.save(user)
    }
}

Ktor — a framework from JetBrains

Kotlin-first framework for creating microservices:

fun Application.module() {
    routing {
        get("/") {
            call.respondText("Hello, Kotlin!")
        }
        
        get("/users/{id}") {
            val id = call.parameters["id"]
            val user = userService.findById(id)
            call.respond(user)
        }
    }
}

Advantages on the server:

• Java compatibility: you can gradually migrate projects

• Performance: same as Java (compiles into JVM bytecode)

• Coroutines: effective work with a large number of requests

• Modern syntax: faster development, easier support

📊 Statistics and popularity

According to the latest developer surveys:

If you are starting to learn Android development or thinking about JVM server development, Kotlin is a great choice. And if you already know Java, switching to Kotlin will be simple and natural.

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