For nearly 20 years, Java was the undisputed king of Android.  

It was the language the system was built on. If you wanted an app, you hired a Java dev. It was reliable, sturdy, and about as exciting as a grey flannel suit.

Then, in 2017, Google announced that Kotlin was also an official language for Android. By 2019, they went further and said Android is now "Kotlin-first."

No, Java is not “deprecated” or going away.

Google’s endorsement didn't happen because Java stopped working. It happened because Java is, to put it politely, "verbose." It’s a language that requires you to say "Please, if it’s not too much trouble, could you perhaps consider opening the door?" while Kotlin just says "Open."

The "Cost of Switching" Anxiety

We know what’s keeping you up, the reason you’re here. You’re worried about:

• Choosing the “wrong” technology

• Being locked into something obscure

• Being able to build all the features you want in the future

• Hiring developers later and discovering nobody wants to touch your codebase

• Paying twice because you picked badly once

That fear is understandable. Early technical decisions can feel permanent.  

Here is the most important thing we can tell you today:  

Kotlin and Java are interoperable.  

They are best friends. You can literally have a Java file and a Kotlin file sitting inside the same app, talking to each other like old neighbors over a fence.  

To put it simply, no matter what language you choose, you are never truly "locked in."  

If you start in Java, we can add Kotlin features later easily.

Java

Java is the older sibling. Calm. Reliable. Sensible shoes.

It’s been used for Android development since the beginning. Millions of apps. Billions of devices. Entire companies built on it.  

Key characteristics:

• Mature, stable, predictable

• Huge global developer pool

• Slightly more verbose (more code to do the same thing)

• Very well understood by tools, libraries, and platforms

Java doesn’t try to be clever. It just… turns up every day and does the job.

Kotlin

Kotlin is newer, but not reckless.

It was designed specifically to improve on Java’s rough edges while staying fully compatible with it. Google officially making Kotlin a first-class language for Android was not a casual decision.  

Key characteristics:

• More concise (less code, fewer mistakes)

• Safer by default (fewer app-crashing surprises)

• Modern features that speed up development

• Fully interoperable with Java (they can live together peacefully)

Kotlin feels like Java after a good night’s sleep and a strong cup of tea.

If you’re not writing the code yourself, you don’t need to care about syntax or clever language features. What you probably care more about are these 5 things:

1. Development speed

2. App stability

3. Hiring and long-term maintenance

4. Cost (now and later)

5. Risk of switching later

1. Development Speed: How Fast Can You Get to Market?

For tight timelines, MVPs and rapid iterations, Kotlin is faster.  

Kotlin is roughly 25-35% more concise than Java.

• Less boilerplate code means features are built faster

• Fewer lines of code means fewer bugs

• Modern tooling integrates beautifully with Android Studio

Imagine you want to create a "User" profile in your app.

• In Java, a developer might have to write 50 lines of boilerplate (repetitive setup stuff that doesn't actually do anything for the user, but the language demands it).

• In Kotlin, that same "User" profile takes about 3 lines.

The Business Impact: Kotlin allows our developers to spend more time building your matchmaking algorithm and less time writing the digital equivalent of "This Page Intentionally Left Blank."

Just know that experience still matters. A good Java team will beat a bad Kotlin team any time. While language choice affects speed, experience affects it more.

2. App Stability: Will it Crash Less?

In the programming world, there is a specific error called a NullPointerException. It’s famous. If you’ve ever had an app randomly die, this is often why. It happens when the code tries to use a piece of information that isn't there.

• Java: Generally lets the developer make this mistake, and the app crashes when the user hits a button.

• Kotlin: Has "Null Safety" baked in. The compiler (the software that checks the code) literally won't let the developer finish the app if there's a risk of this crash.

The Verdict: Kotlin is like a car that won't let you put it in gear unless your seatbelt is on. Java assumes you're a professional and lets you drive straight into a problem if you forget.

This doesn’t mean that Java apps are unstable. It only means Kotlin gives developers more guardrails.

3. Hiring Kotlin Developers: Will You Regret it Later?

Let’s be clear:

• Java developers are everywhere

• Kotlin developers are increasingly everywhere

• Most professional Android developers today can work with both

Because Kotlin and Java interoperate, you are not locking yourself into a niche.

In fact, many Android codebases today are mixed:

• Older Java code

• Newer Kotlin features layered on top

This is completely normal.

If you look at the "Kotlin vs Java" landscape in 2026 and beyond, the trend is clear. Most new, high-end Android developers prefer Kotlin. It’s modern, it’s fast, and it’s what Google uses for its own apps.

However, Java is the "Old Guard." There are millions of Java developers globally. If you’re building a massive, enterprise-grade banking system that needs to stay exactly the same for the next 40 years, Java’s "boring" stability is actually a feature, not a bug.

4. Cost: Will it Be Expensive?

Short term:

• Kotlin can slightly reduce development time

• Fewer bugs can mean lower QA and maintenance costs

Long term:

• Java has proven longevity

• Kotlin is now deeply embedded in Android’s future

The real cost risk is not the language. It’s unclear requirements, rushed decisions, and poor architecture.

A well-built Java app ages better than a poorly built Kotlin one.

A well-built Kotlin app ages better than both.

5. Interoperability: Will We Need to Switch Later?

You almost never need to fully switch.

Because Kotlin runs on the same JVM and works seamlessly with Java:

• You can introduce Kotlin gradually

• You can modernise parts without rewriting everything

• You’re not trapped

This is one of the most misunderstood parts of the Kotlin vs Java debate.

You’re choosing a primary language, not burning a bridge.

As a development outsourcing agency for both Kotlin and Java, we promise no bias, so here is our honest, expert take:

Choose Java if...

• You have an existing app written in Java and you just want to tweak it.

• Your development team consists of old school enterprise developers who have 20 years of Java experience and haven't touched Kotlin.

• You are building something incredibly low-level where every millisecond of "compile time" (the time it takes to turn code into an app) matters to your internal team.

• You value maximum predictability and familiarity

• The app is stable, mature, and evolving slowly

Choose Kotlin if...

• You are starting a brand new app. (This is the 90% use case).

• You want your app to be "future-proof." Google’s latest UI tool, Jetpack Compose, is built specifically for Kotlin.

• You want a faster time to market. Because there is less code to write, we can often get a prototype in your hands sooner.

• You want a more stable app with fewer "random" crashes.

Choose Either if...

• You’re working with an experienced Android development agency

• Your requirements are clear

• Long-term maintainability is prioritised over trends

Choosing between Kotlin vs Java feels like a life-altering decision, but in reality, it’s about choosing the right tool for your specific journey.  

If you’re building the next big social media platform or a sleek e-commerce tool, Kotlin is the way to go. It’s what we use here at the agency because it makes our lives better and your app more robust.

But if you have a specific reason to stay with the Grandfather of Android (Java), we can do that too. The magic isn't in the language; it’s in the product we build together.