Kotlin vs Java for Android Development: Why I Chose Kotlin (And You Should Too)

My Background: From C/C++ to Mobile

I spent years writing C and C++ code before transitioning to mobile development. When I decided to focus on Android, the big question was: Kotlin or Java? Here's why I chose Kotlin, and why you should consider it too.

The Current State (2025)

Let's be clear: Kotlin is the official recommended language for Android development. Google announced this in 2019, and by 2025, it's the clear winner:

• 80%+ of professional Android apps use Kotlin
• All new Google Android samples are Kotlin-first
• Jetpack libraries designed for Kotlin
• New Android features often Kotlin-exclusive initially
• Job postings predominantly require Kotlin

Kotlin Advantages

1. Null Safety

Coming from C/C++, null pointer crashes were my nightmare. Kotlin solved this elegantly:

// Java - NullPointerException waiting to happen
String name = user.getName();
int length = name.length(); // Crash if name is null

// Kotlin - Compiler prevents null pointer errors
val name: String? = user.name
val length = name?.length ?: 0 // Safe, returns 0 if null

2. Concise Syntax

Kotlin eliminates Java's verbosity. Compare data classes:

// Java - Lots of boilerplate
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; }
    
    @Override
    public boolean equals(Object o) { /* ... */ }
    @Override
    public int hashCode() { /* ... */ }
}

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

3. Coroutines for Async Code

Kotlin coroutines make asynchronous code readable:

// Java - Callback hell
api.fetchUser(userId, new Callback() {
    @Override
    public void onSuccess(User user) {
        api.fetchPosts(user.getId(), new Callback() {
            @Override
            public void onSuccess(List posts) {
                // Finally do something
            }
        });
    }
});

// Kotlin - Sequential and clean
suspend fun loadUserPosts() {
    val user = api.fetchUser(userId)
    val posts = api.fetchPosts(user.id)
    // Clean, readable, no callbacks
}

4. Extension Functions

Add functionality to existing classes without inheritance:

// Add function to String class
fun String.isValidEmail(): Boolean {
    return android.util.Patterns.EMAIL_ADDRESS.matcher(this).matches()
}

// Usage
val email = "user@example.com"
if (email.isValidEmail()) {
    // Process email
}

5. Smart Casts

No more redundant casting:

// Java
if (obj instanceof String) {
    String str = (String) obj; // Redundant cast
    int length = str.length();
}

// Kotlin
if (obj is String) {
    val length = obj.length // Automatically cast
}

When Java Might Make Sense

To be fair, Java still has some use cases:

• Legacy codebases - Maintaining old Java apps
• Team expertise - Entire team only knows Java (though learning Kotlin is quick)
• Library compatibility - Some very old libraries (rare in 2025)

But honestly? These are edge cases. For new projects in 2025, Kotlin is the obvious choice.

Learning Curve: Easier Than You Think

Coming from C/C++, I found Kotlin's learning curve surprisingly gentle:

• Week 1: Basic syntax, variables, functions
• Week 2: Classes, objects, null safety
• Week 3: Collections, lambdas, higher-order functions
• Week 4: Coroutines, Flow, advanced features

If you know Java, you can be productive in Kotlin within days. If you're coming from other languages, it's still faster to learn than Java.

Job Market Reality

Job Postings Analysis (2025):

• Kotlin Required: 75% of Android jobs
• Kotlin Preferred: 20% of Android jobs
• Java Only: 5% (mostly legacy maintenance)

Salary Comparison:

• Kotlin developers: Average $120k/year
• Java-only Android devs: Average $95k/year

The market has spoken: Kotlin skills are more valuable.

My Experience Building Apps

I've built multiple apps in Kotlin (EasyCCTV, Lists And Notes) and the experience has been consistently positive:

• Fewer crashes due to null safety
• Faster development with concise syntax
• Easier maintenance and refactoring
• Better integration with modern Android libraries
• More enjoyable to write

The Verdict

Choose Kotlin if:

• Starting a new Android project (do this)
• Learning Android development (do this)
• Want modern, clean code (do this)
• Care about career prospects (do this)

Stick with Java only if:

• Maintaining legacy codebase
• Team refuses to learn (bad sign)
• Building for Android 4.x devices (why?)

Getting Started with Kotlin

Resources I Recommend:

1. Kotlin Koans - Interactive exercises
2. Android Developer Docs - Official Kotlin guides
3. Kotlin for Java Developers - If transitioning
4. Build real projects - Best way to learn

Conclusion

The Kotlin vs Java debate is essentially over. Kotlin won. It's more concise, safer, more modern, and backed by Google and JetBrains. Unless you have a specific reason to use Java, choose Kotlin for Android development in 2025.

After building multiple Kotlin apps and seeing the difference firsthand, I can't imagine going back to Java for Android development. The productivity boost and code quality improvements are too significant to ignore.

Ready to build your Android app with modern Kotlin? I'm available for freelance projects and consultations. Let's talk.