Java vs. Kotlin: which one to choose in 2025?

For decades, Java has been considered the king of backend development and Android applications. But with the advent of Kotlin, everything changed: Google officially recognized it as the main language for Android, and large companies began to translate their projects.

So which language to choose in 2025: classic Java or modern Kotlin? Let's take a deep dive, but let's get down to business 👇

🧠 1. Brief and expressive syntax

Java:

public class User {
  private String name;
  public User(String name) {
    this.name = name;
  }
  public String getName() {
    return name;
  }
}

Kotlin:

data class User(val name: String)

💡 Kotlin allows you to write 2-3 times less code, keeping the same logic.

This is achieved through concise syntax and built-in language capabilities. For example, Kotlin has data class, which automatically creates getters, equals(), hashCode() and toString() — whereas in Java you would have to write all this manually.
In addition, in Kotlin there is no need to constantly write getters/setters, type declarations can often be displayed automatically, and constructions like when, smart cast, default arguments, named arguments and extension functions make the code shorter, clearer and easier to read.
Less template code means faster development and a lower chance of bugs.

🚨 2. Null safety

Java still suffers from NullPointerException — one of the most common sources of errors.

Kotlin has built protection right into the language:

val name: String? = null
println(name?.length)

🔥 Kotlin forces you to think about nulls — and that's good.

⚙️ 3. Support and compatibility

🚀 4. Modern Kotlin features

• Extension functions

• Smart casts

• Coroutines (asynchronous)

• data classes, sealed classes, delegation, etc.

Java is also evolving (especially with Java 17 and 21), but Kotlin is faster at implementing modern ideas.
The latest versions of Java have indeed introduced important innovations: record-classes, sealed-types, switch as an expression, improvements in working with streams (virtual threads in Project Loom) and pattern matching. This makes Java noticeably more modern than before.

However, Kotlin was originally designed as a compact and expressive language, and new features appear in it faster, easier to use and better integrated with each other. For example, while Java is only implementing records, Kotlin data class has long been the standard. While Java is taking steps towards coroutines through virtual streams, in Kotlin suspend and coroutines are already actively used in combat projects.

💼 5. What do companies choose in 2025?

• Android: 70% of new projects are in Kotlin

• Backend: Java is consistently popular, but Kotlin is growing

• Fintech and corporations: more often stay on Java

• Startups: actively choose Kotlin

🧑‍💻 6. Who is each language suitable for?

✅ Java:

• For stable, scalable solutions

• If you are in the corporate sector

• When working with existing code

✅ Kotlin:

• Do you want to write quickly and in a modern way?

• You like clean and compact code

• Do you work with Android or startups?

📚 Do you want to delve into the topic?

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